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PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Components Of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Amortization: |  |  |
Relating to assets sold during the period | $ 4.8 | $ 3.3 |
Pension Benefits [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service cost | 17.1 | 17.6 | $ 22.7
Interest cost | (30.5) | (30.3) | (37.7)
Expected return on plan assets | (54.5) | (54.7) | (59.8)
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) | 22.3 | 21.1 | 20.8
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment | 0.0 | 0.0 | 0.2
Amortization: |  |  |
Amortization of prior service (cost) credit | (2.6) | (2.2) | (2.3)
Net actuarial loss | 22.3 | 21.1 | 21.0
Net periodic benefit cost | 18.0 | 16.5 | 23.9
Effect of Curtailment | 0.0 | 0.0 | (1.2)
Current year actuarial (gain)/loss | 9.3 | 37.8 | (0.7)
Amortization of net loss | 22.3 | 21.1 | 21.0
Current year prior service cost | 0.0 | 5.7 | 0.0
Amortization of prior service (cost) credit | (2.6) | (2.2) | (2.3)
Total recognized in other comprehensive income | (15.6) | 20.2 | (25.2)
Total recognized in net periodic cost and other comprehensive income | 2.4 | 36.7 | (1.3)
Defined Benefit Plan, Benefit Obligation | (973.1) | (931.6) | (910.8)
Defined Benefit Plan, Funded (Unfunded) Status of Plan | (223.3) | (245.8) |
Other Benefits [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service cost | 1.8 | 1.7 | 6.4
Interest cost | (8.3) | (9.1) | (13.4)
Expected return on plan assets | (17.7) | (17.1) | (18.3)
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) | 4.5 | 6.0 | 6.6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment | 0.0 | 0.0 | 0.0
Amortization: |  |  |
Amortization of prior service (cost) credit | 3.0 | 3.7 | 3.7
Net actuarial loss | 4.5 | 6.0 | 6.6
Net periodic benefit cost | (6.1) | (4.0) | 4.4
Effect of Curtailment | 0.0 | 0.0 | 0.0
Current year actuarial (gain)/loss | 1.2 | (8.1) | 0.2
Amortization of net loss | 4.5 | 6.0 | 6.6
Current year prior service cost | 0.0 | 9.8 | 0.0
Amortization of prior service (cost) credit | 3.0 | 3.7 | 3.7
Total recognized in other comprehensive income | (0.3) | (0.6) | (2.7)
Total recognized in net periodic cost and other comprehensive income | (6.4) | (4.6) | 1.7
Defined Benefit Plan, Benefit Obligation | (265.9) | (264.6) | $ (266.0)
Defined Benefit Plan, Funded (Unfunded) Status of Plan | (3.4) | (11.6) |
Salaried Employees [Member] | Pension Benefits [Member] |  |  |
Amortization: |  |  |
Defined Benefit Plan, Benefit Obligation | (368.0) | (351.9) |
Defined Benefit Plan, Funded (Unfunded) Status of Plan | (98.6) | (109.0) |
Salaried Employees [Member] | Other Benefits [Member] |  |  |
Amortization: |  |  |
Defined Benefit Plan, Benefit Obligation | (37.7) | (37.6) |
Defined Benefit Plan, Funded (Unfunded) Status of Plan | (37.7) | (37.6) |
Hourly Employees [Member] | Pension Benefits [Member] |  |  |
Amortization: |  |  |
Defined Benefit Plan, Benefit Obligation | (590.0) | (565.6) |
Defined Benefit Plan, Funded (Unfunded) Status of Plan | (117.0) | (128.7) |
Hourly Employees [Member] | Other Benefits [Member] |  |  |
Amortization: |  |  |
Defined Benefit Plan, Benefit Obligation | (228.2) | (227.0) |
Defined Benefit Plan, Funded (Unfunded) Status of Plan | 34.3 | 26.0 |
Mining Employees [Member] | Pension Benefits [Member] |  |  |
Amortization: |  |  |
Defined Benefit Plan, Benefit Obligation | (10.3) | (10.0) |
Defined Benefit Plan, Funded (Unfunded) Status of Plan | (2.9) | (4.0) |
Supplemental Executive Retirement Plan S E R P [Member] | Pension Benefits [Member] |  |  |
Amortization: |  |  |
Defined Benefit Plan, Benefit Obligation | (4.8) | (4.1) |
Defined Benefit Plan, Funded (Unfunded) Status of Plan | $ (4.8) | $ (4.1) |

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