CONDENSED CONSOLIDATED INCOME STATEMENTS - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Operating revenues	$ 1,746.5	$ 1,651.0	$ 6,114.1	$ 5,308.3
Operating expenses
Cost of sales	560.7	482.8	2,352.2	1,662.0
Other operation and maintenance	473.7	498.7	1,417.4	1,427.5
Depreciation and amortization	271.6	245.0	799.2	726.6
Property and revenue taxes	50.5	54.3	157.2	156.6
Total operating expenses	1,356.5	1,280.8	4,726.0	3,972.7
Operating income	390.0	370.2	1,388.1	1,335.6
Equity in earnings of transmission affiliates	42.3	40.1	126.2	132.8
Other income, net	25.2	25.7	97.7	59.9
Interest expense	118.0	122.0	357.5	375.8
Other expense	(50.5)	(56.2)	(133.6)	(183.1)
Income before income taxes	339.5	314.0	1,254.5	1,152.5
Income tax expense	50.8	46.9	179.8	190.7
Net income	288.7	267.1	1,074.7	961.8
Preferred stock dividends of subsidiary	0.3	0.3	0.9	0.9
Net loss attributable to noncontrolling interests	(1.6)	0.0	(2.3)	0.0
Net income attributed to common shareholders	$ 290.0	$ 266.8	$ 1,076.1	$ 960.9
Earnings per share
Basic (in dollars per share)	$ 0.92	$ 0.85	$ 3.41	$ 3.05
Diluted (in dollars per share)	$ 0.92	$ 0.84	$ 3.40	$ 3.04
Weighted average common shares outstanding
Basic (in shares)	315.4	315.4	315.4	315.4
Diluted (in shares)	316.3	316.5	316.3	316.6