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Annual report pursuant to Section 13 and 15(d)

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Benefit Obligations, Fair Value of Plan Assets, and Net Funded Status) (Details)

v3.6.0.2
PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Benefit Obligations, Fair Value of Plan Assets, and Net Funded Status) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Fair value of plan assets — beginning of year $ 193.4 $ 188.1 Ìý Ìý Ìý
Employer contributions 1.1 3.5 Ìý Ìý Ìý
Fair value of plan assets — end of year 202.4 193.4 $ 188.1 Ìý Ìý
Funded status at December 31: Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Fair Value of Plan Assets 193.4 188.1 188.1 $ 202.4 $ 193.4
Amounts recognized in Statements of Financial Position: Ìý Ìý Ìý Ìý Ìý
Assets, Current Ìý Ìý Ìý 824.6 982.7
Noncurrent liabilities Ìý Ìý Ìý (280.5) (221.0)
Pension Benefits [Member] Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Benefit obligations — beginning of year (910.8) (998.0) Ìý Ìý Ìý
Service cost (excluding expenses) 17.6 22.7 26.1 Ìý Ìý
Interest cost 30.3 37.7 40.3 Ìý Ìý
Plan amendments 5.7 0.0 Ìý Ìý Ìý
Actuarial loss (21.1) (20.8) (14.0) Ìý Ìý
Defined Benefit Plan, Change in Actuarial (gain) loss 38.1 (67.7) Ìý Ìý Ìý
Benefits paid (70.9) (78.7) Ìý Ìý Ìý
Participant contributions 0.0 0.0 Ìý Ìý Ìý
Federal subsidy on benefits paid 0.0 0.0 Ìý Ìý Ìý
Benefit obligations — end of year (931.6) (910.8) (998.0) Ìý Ìý
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Fair value of plan assets — beginning of year 700.6 749.8 Ìý Ìý Ìý
Actual return on plan assets 54.8 (6.4) 59.1 Ìý Ìý
Participant contributions 0.0 0.0 Ìý Ìý Ìý
Employer contributions 1.2 35.7 Ìý Ìý Ìý
Assets Transferred to (from) Plan 0.1 0.2 Ìý Ìý Ìý
Fair value of plan assets — end of year 685.8 700.6 749.8 Ìý Ìý
Funded status at December 31: Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Fair Value of Plan Assets 700.6 749.8 749.8 685.8 700.6
Defined Benefit Plan, Benefit Obligation (910.8) (998.0) (998.0) (931.6) (910.8)
Defined Benefit Plan, Funded Status of Plan Ìý Ìý Ìý (245.8) (210.2)
Total amount recognized Ìý Ìý Ìý (245.8) (210.2)
Amounts recognized in Statements of Financial Position: Ìý Ìý Ìý Ìý Ìý
Assets, Current Ìý Ìý Ìý 0.0 0.0
Current liabilities Ìý Ìý Ìý (0.1) (0.5)
Noncurrent liabilities Ìý Ìý Ìý (245.7) (209.7)
Total amount recognized Ìý Ìý Ìý (245.8) (210.2)
Amounts recognized in accumulated other comprehensive income: Ìý Ìý Ìý Ìý Ìý
Prior service cost Ìý Ìý Ìý 11.0 7.5
Net actuarial loss Ìý Ìý Ìý 315.9 290.9
Net amount recognized Ìý Ìý Ìý 326.9 298.4
The estimated amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost: Ìý Ìý Ìý Ìý Ìý
Net actuarial loss 21.1 Ìý Ìý Ìý Ìý
Prior service cost 2.6 Ìý Ìý Ìý Ìý
Net amount recognized 23.7 Ìý Ìý Ìý Ìý
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments 0.0 (1.2) Ìý Ìý Ìý
Other Benefits [Member] Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Benefit obligations — beginning of year (266.0) (295.8) Ìý Ìý Ìý
Service cost (excluding expenses) 1.7 6.4 1.8 Ìý Ìý
Interest cost 9.1 13.4 11.9 Ìý Ìý
Plan amendments 9.8 0.0 Ìý Ìý Ìý
Actuarial loss (6.0) (6.6) (4.5) Ìý Ìý
Defined Benefit Plan, Change in Actuarial (gain) loss (7.2) (27.0) Ìý Ìý Ìý
Benefits paid (21.3) (20.6) Ìý Ìý Ìý
Participant contributions 6.0 4.0 Ìý Ìý Ìý
Federal subsidy on benefits paid 0.5 0.4 Ìý Ìý Ìý
Benefit obligations — end of year (264.6) (266.0) (295.8) Ìý Ìý
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Fair value of plan assets — beginning of year 250.6 269.3 Ìý Ìý Ìý
Actual return on plan assets 16.0 (3.9) 31.9 Ìý Ìý
Participant contributions 0.5 0.4 Ìý Ìý Ìý
Employer contributions 1.7 1.3 Ìý Ìý Ìý
Assets Transferred to (from) Plan 0.0 0.0 Ìý Ìý Ìý
Benefits paid (15.8) (16.5) Ìý Ìý Ìý
Fair value of plan assets — end of year 253.0 250.6 269.3 Ìý Ìý
Funded status at December 31: Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Fair Value of Plan Assets 250.6 269.3 269.3 253.0 250.6
Defined Benefit Plan, Benefit Obligation (266.0) (295.8) $ (295.8) (264.6) (266.0)
Defined Benefit Plan, Funded Status of Plan Ìý Ìý Ìý (11.6) (15.4)
Total amount recognized Ìý Ìý Ìý (11.6) (15.4)
Amounts recognized in Statements of Financial Position: Ìý Ìý Ìý Ìý Ìý
Assets, Current Ìý Ìý Ìý Ìý 0.0
Assets, Noncurrent Ìý Ìý Ìý 27.3 Ìý
Current liabilities Ìý Ìý Ìý (4.1) (4.1)
Noncurrent liabilities Ìý Ìý Ìý (34.8) (11.3)
Total amount recognized Ìý Ìý Ìý (11.6) (15.4)
Amounts recognized in accumulated other comprehensive income: Ìý Ìý Ìý Ìý Ìý
Prior service cost Ìý Ìý Ìý (26.9) (39.5)
Net actuarial loss Ìý Ìý Ìý 87.0 91.5
Net amount recognized Ìý Ìý Ìý 60.1 52.0
The estimated amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost: Ìý Ìý Ìý Ìý Ìý
Net actuarial loss 5.0 Ìý Ìý Ìý Ìý
Prior service cost (3.0) Ìý Ìý Ìý Ìý
Net amount recognized 2.0 Ìý Ìý Ìý Ìý
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments 0.0 0.0 Ìý Ìý Ìý
Salaried Employees [Member] | Pension Benefits [Member] Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Benefit obligations — beginning of year (340.0) Ìý Ìý Ìý Ìý
Benefit obligations — end of year (351.9) (340.0) Ìý Ìý Ìý
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Fair value of plan assets — beginning of year 258.3 Ìý Ìý Ìý Ìý
Fair value of plan assets — end of year 242.9 258.3 Ìý Ìý Ìý
Funded status at December 31: Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Fair Value of Plan Assets 258.3 258.3 Ìý 242.9 258.3
Defined Benefit Plan, Benefit Obligation (340.0) (340.0) Ìý (351.9) (340.0)
Defined Benefit Plan, Funded Status of Plan Ìý Ìý Ìý (109.0) (81.7)
Salaried Employees [Member] | Other Benefits [Member] Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Benefit obligations — beginning of year (38.2) Ìý Ìý Ìý Ìý
Benefit obligations — end of year (37.6) (38.2) Ìý Ìý Ìý
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Fair value of plan assets — beginning of year 0.0 Ìý Ìý Ìý Ìý
Fair value of plan assets — end of year 0.0 0.0 Ìý Ìý Ìý
Funded status at December 31: Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Fair Value of Plan Assets 0.0 0.0 Ìý 0.0 0.0
Defined Benefit Plan, Benefit Obligation (38.2) (38.2) Ìý (37.6) (38.2)
Defined Benefit Plan, Funded Status of Plan Ìý Ìý Ìý (37.6) (38.2)
Hourly Employees [Member] | Pension Benefits [Member] Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Benefit obligations — beginning of year (558.6) Ìý Ìý Ìý Ìý
Benefit obligations — end of year (565.6) (558.6) Ìý Ìý Ìý
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Fair value of plan assets — beginning of year 436.7 Ìý Ìý Ìý Ìý
Fair value of plan assets — end of year 436.9 436.7 Ìý Ìý Ìý
Funded status at December 31: Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Fair Value of Plan Assets 436.7 436.7 Ìý 436.9 436.7
Defined Benefit Plan, Benefit Obligation (558.6) (558.6) Ìý (565.6) (558.6)
Defined Benefit Plan, Funded Status of Plan Ìý Ìý Ìý (128.7) (121.9)
Hourly Employees [Member] | Other Benefits [Member] Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Benefit obligations — beginning of year (227.8) Ìý Ìý Ìý Ìý
Benefit obligations — end of year (227.0) (227.8) Ìý Ìý Ìý
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Fair value of plan assets — beginning of year 250.6 Ìý Ìý Ìý Ìý
Fair value of plan assets — end of year 253.0 250.6 Ìý Ìý Ìý
Funded status at December 31: Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Fair Value of Plan Assets 250.6 250.6 Ìý 253.0 250.6
Defined Benefit Plan, Benefit Obligation (227.8) (227.8) Ìý (227.0) (227.8)
Defined Benefit Plan, Funded Status of Plan Ìý Ìý Ìý 26.0 22.8
Mining Employees [Member] | Pension Benefits [Member] Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Benefit obligations — beginning of year (8.6) Ìý Ìý Ìý Ìý
Benefit obligations — end of year (10.0) (8.6) Ìý Ìý Ìý
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Fair value of plan assets — beginning of year 5.6 Ìý Ìý Ìý Ìý
Fair value of plan assets — end of year 6.0 5.6 Ìý Ìý Ìý
Funded status at December 31: Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Fair Value of Plan Assets 5.6 5.6 Ìý 6.0 5.6
Defined Benefit Plan, Benefit Obligation (8.6) (8.6) Ìý (10.0) (8.6)
Defined Benefit Plan, Funded Status of Plan Ìý Ìý Ìý (4.0) (3.0)
Supplemental Executive Retirement Plan S E R P [Member] | Pension Benefits [Member] Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Benefit obligations — beginning of year (3.6) Ìý Ìý Ìý Ìý
Benefit obligations — end of year (4.1) (3.6) Ìý Ìý Ìý
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Fair value of plan assets — beginning of year 0.0 Ìý Ìý Ìý Ìý
Fair value of plan assets — end of year 0.0 0.0 Ìý Ìý Ìý
Funded status at December 31: Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Fair Value of Plan Assets 0.0 0.0 Ìý 0.0 0.0
Defined Benefit Plan, Benefit Obligation (3.6) (3.6) Ìý (4.1) (3.6)
Defined Benefit Plan, Funded Status of Plan Ìý Ìý Ìý $ (4.1) $ (3.6)
Pension Costs [Member] | Pension Benefits [Member] Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Service cost (excluding expenses) 17.6 22.7 Ìý Ìý Ìý
Interest cost 30.3 37.7 Ìý Ìý Ìý
Pension Costs [Member] | Other Benefits [Member] Ìý Ìý Ìý Ìý Ìý
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Ìý Ìý Ìý Ìý Ìý
Service cost (excluding expenses) 1.7 1.9 Ìý Ìý Ìý
Interest cost $ 9.1 $ 11.5 Ìý Ìý Ìý