CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Statement of Other Comprehensive Income [Abstract]
Net income	$ 243.0	$ 210.0	$ 968.5	$ 832.6
Derivatives accounted for as cash flow hedges
Reclassification of realized derivative gains to net income, net of tax	(0.1)	0.0	(0.2)	(0.1)
Defined benefit plans
Amortization of pension and OPEB costs included in net periodic benefit cost, net of tax	0.1	0.0	0.1	0.0
Other comprehensive loss, net of tax	0.0	0.0	(0.1)	(0.1)
Comprehensive income	243.0	210.0	968.4	832.5
Preferred stock dividends of subsidiary	0.3	0.3	0.6	0.6
Comprehensive loss attributed to noncontrolling interests	2.7	1.6	1.7	1.6
Comprehensive income attributed to common shareholders	$ 245.4	$ 211.3	$ 969.5	$ 833.5