Consolidated Income Statements - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Operating revenues	$ 8,316.0	$ 7,241.7	$ 7,523.1
Operating expenses
Cost of sales	3,311.0	2,319.5	2,678.8
Other operation and maintenance	2,005.5	2,032.2	2,184.8
Depreciation and amortization	1,074.3	975.9	926.3
Property and revenue taxes	210.3	208.0	201.8
Total operating expenses	6,601.1	5,535.6	5,991.7
Operating income	1,714.9	1,706.1	1,531.4
Equity in earnings of transmission affiliates	158.1	175.8	127.6
Other income, net	133.2	79.5	102.2
Interest expense	471.1	493.7	501.5
Loss on debt extinguishment	36.3	38.4	0.0
Other expense	(216.1)	(276.8)	(271.7)
Income before income taxes	1,498.8	1,429.3	1,259.7
Income tax expense	200.3	227.9	125.0
Net income	1,298.5	1,201.4	1,134.7
Preferred stock dividends of subsidiary	1.2	1.2	1.2
Net (income) loss attributed to noncontrolling interests	3.0	(0.3)	0.5
Net income attributed to common shareholders	$ 1,300.3	$ 1,199.9	$ 1,134.0
Earnings per share
Basic (in dollars per share)	$ 4.12	$ 3.80	$ 3.60
Diluted (in dollars per share)	$ 4.11	$ 3.79	$ 3.58
Weighted average common shares outstanding
Basic (in shares)	315.4	315.4	315.4
Diluted (in shares)	316.3	316.5	316.7