Statements of Consolidated Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ (292.2)us-gaap_NetIncomeLoss	$ 15.8us-gaap_NetIncomeLoss
Reclassification adjustments:
Amortization of net actuarial (gain) loss	0.3	(0.3)
Amortization of prior service cost	0.7	2.8
Other Comprehensive Income (Loss), Finalization of Pension and Other Postretirement Benefit Plan Valuation, before Tax	106.6	0
Other comprehensive income relating to VEBAs	107.6	2.5
Available for sale securities:
Unrealized gain on available for sale securities	0	0.1
Reclassification adjustments:
Reclassification of unrealized gain upon sale of available for sale securities	0.1	(0.1)
Other comprehensive income (loss) relating to available for sale securities	0.1	0
Foreign currency translation adjustment	0.1	0.2
Other comprehensive income, before tax	107.8	2.7
Income tax expense related to items of other comprehensive income	(40.9)	(1.8)
Other comprehensive income, net of tax	66.9	0.9
Comprehensive income	$ (225.3)us-gaap_ComprehensiveIncomeNetOfTax	$ 16.7us-gaap_ComprehensiveIncomeNetOfTax

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Amount before tax of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) related to pension and other postretirement benefit plans.

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Amount before tax, after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Amount before tax of gain (loss) adjustment to other comprehensive income (loss) resulting from settlement or curtailment of defined benefit pension and other postretirement defined benefit plans.

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Amount before tax, after reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount before tax, after reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans.

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Amount before tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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Amount before tax of reclassification adjustment from accumulated other comprehensive income (loss) for actuarial gain (loss) related to pension and other postretirement benefit plans.

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