CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 367.4	$ (116.7)
Pension and other postretirement plans adjustments:
Amortization of prior service costs	0.0	0.1
Amortization of actuarial losses	0.1	0.1
Net curtailment (1)		(0.4)
Other comprehensive income (loss)	0.1	(0.2)
Comprehensive income (loss)	$ 367.5	$ (116.9)

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, after tax, of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) of defined benefit plan.

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