CONDENSED CONSOLIDATED INCOME STATEMENTS - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Operating revenues	$ 2,691.4	$ 2,108.6
Operating expenses
Cost of sales	1,265.6	734.7
Other operation and maintenance	479.9	455.7
Depreciation and amortization	261.4	239.1
Property and revenue taxes	55.2	52.5
Total operating expenses	2,062.1	1,482.0
Operating income	629.3	626.6
Equity in earnings of transmission affiliates	42.6	39.8
Other income, net	32.8	5.6
Interest expense	119.5	129.4
Other expense	(44.1)	(84.0)
Income before income taxes	585.2	542.6
Income tax expense (benefit)	74.9	90.0
Net income	510.3	452.6
Preferred stock dividends of subsidiary	0.3	0.3
Net loss attributable to noncontrolling interests	(0.1)	(0.2)
Net income attributed to common shareholders	$ 510.1	$ 452.5
Earnings per share
Basic (in dollars per share)	$ 1.62	$ 1.43
Diluted (in dollars per share)	$ 1.61	$ 1.43
Weighted average common shares outstanding
Basic (in shares)	315.4	315.4
Diluted (in shares)	316.2	316.7