STATEMENTS OF CONSOLIDATED COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 4.5	$ 29.1
Other comprehensive income (loss), net of tax
Defined benefit pension plan and Salaried VEBA	0.7	1.1
Available for sale securities		(0.2)
Cash flow hedges	8.5	(15.9)
Fair value hedges		(0.5)
Foreign currency translation	(0.1)
Other comprehensive income (loss), net of tax	9.1	(15.5)
Comprehensive income	$ 13.6	$ 13.6

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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