CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Statement of Other Comprehensive Income [Abstract]
Net income	$ 568.0	$ 510.3
Derivatives accounted for as cash flow hedges
Reclassification of realized net derivative (gain) loss to net income, net of tax	(0.1)	1.0
Cash flow hedges, net	(0.1)	1.0
Defined benefit plans
Amortization of pension and OPEB costs included in net periodic benefit cost, net of tax	0.1	0.1
Other comprehensive income, net of tax	0.0	1.1
Comprehensive income	568.0	511.4
Preferred stock dividends of subsidiary	0.3	0.3
Comprehensive (income) loss attributed to noncontrolling interests	(1.8)	0.1
Comprehensive income attributed to common shareholders	$ 565.9	$ 511.2