Consolidated Income Statements - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Statement [Abstract]
Operating revenues	$ 8,893.0	$ 9,597.4	$ 8,316.0
Operating expenses
Cost of sales	3,191.2	4,358.9	3,311.0
Other operation and maintenance	2,100.5	1,938.0	2,005.5
Impairment related to ICC disallowances	178.9	0.0	0.0
Depreciation and amortization	1,264.2	1,122.6	1,074.3
Property and revenue taxes	250.2	253.7	210.3
Total operating expenses	6,985.0	7,673.2	6,601.1
Operating income	1,908.0	1,924.2	1,714.9
Equity in earnings of transmission affiliates	177.5	194.7	158.1
Other income, net	177.7	128.8	133.2
Interest expense	726.9	515.1	471.1
Loss on debt extinguishment	0.0	0.0	36.3
Other expense	(371.7)	(191.6)	(216.1)
Income before income taxes	1,536.3	1,732.6	1,498.8
Income tax expense	204.6	322.9	200.3
Net income	1,331.7	1,409.7	1,298.5
Preferred stock dividends of subsidiary	1.2	1.2	1.2
Net (income) loss attributed to noncontrolling interests	1.2	(0.4)	3.0
Net income attributed to common shareholders	$ 1,331.7	$ 1,408.1	$ 1,300.3
Earnings per share
Basic (in dollars per share)	$ 4.22	$ 4.46	$ 4.12
Diluted (in dollars per share)	$ 4.22	$ 4.45	$ 4.11
Weighted average common shares outstanding
Basic (in shares)	315.4	315.4	315.4
Diluted (in shares)	315.9	316.1	316.3