Segment Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) numberOfSegments	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Segment information
Number of reportable segments | numberOfSegments	6
Operating revenues	$ 8,599.9	$ 8,893.0	$ 9,597.4
Fuel and purchased power	1,455.7	1,615.9	1,881.4
Cost of natural gas sold	1,200.3	1,575.3	2,477.5
Other operation and maintenance	2,158.0	2,100.5	1,938.0
Impairment related to ICC disallowances	12.1	178.9	0.0
Depreciation and amortization	1,354.5	1,264.2	1,122.6
Property and revenue taxes	266.5	250.2	253.7
Equity in earnings of transmission affiliates	207.5	177.5	194.7
Other income, net	178.2	177.7	128.8
Interest expense	815.3	727.4	515.1
Gain on debt extinguishments	(23.1)	(0.5)	0.0
Income tax expense (benefit)	222.0	204.6	322.9
Preferred stock dividends of subsidiary	1.2	1.2	1.2
Net (income) loss attributed to noncontrolling interests	4.1	1.2	(0.4)
Net income (loss) attributed to common shareholders	1,527.2	1,331.7	1,408.1
Capital expenditures and asset acquisitions	3,774.8	3,507.9	2,696.9
Equity method investments	2,191.6	2,081.6	1,981.9
Total assets	47,363.2	43,939.7	41,872.1
Reconciling eliminations
Segment information
Fuel and purchased power	0.0	0.0	0.0
Cost of natural gas sold	(46.0)	(60.1)	(51.9)
Other operation and maintenance	(9.1)	(9.1)	(9.1)
Impairment related to ICC disallowances	0.0	0.0
Depreciation and amortization	(88.5)	(77.5)	(68.1)
Property and revenue taxes	0.0	0.0	0.0
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Other income, net	(31.7)	(20.5)	(2.3)
Interest expense	(362.2)	(350.2)	(336.2)
Gain on debt extinguishments	0.0	0.0
Income tax expense (benefit)	0.0	0.0	0.0
Preferred stock dividends of subsidiary	0.0	0.0	0.0
Net (income) loss attributed to noncontrolling interests	0.0	0.0	0.0
Net income (loss) attributed to common shareholders	0.0	0.0	0.0
Capital expenditures and asset acquisitions	0.0	0.0	0.0
Equity method investments	0.0	0.0	0.0
Total assets	(3,553.6)	(3,640.1)	(3,256.5)
Reconciling eliminations | WE
Segment information
Total assets	1,525.4	1,630.6	1,632.9
Wisconsin | Operating segments
Segment information
Operating revenues	6,330.5	6,625.9	6,960.5
Illinois | Operating segments
Segment information
Operating revenues	1,602.4	1,557.8	1,890.9
Other States | Operating segments
Segment information
Operating revenues	449.8	519.1	618.5
Electric transmission | Operating segments
Segment information
Fuel and purchased power	0.0	0.0	0.0
Cost of natural gas sold	0.0	0.0	0.0
Other operation and maintenance	0.0	0.0	0.0
Impairment related to ICC disallowances	0.0	0.0
Depreciation and amortization	0.0	0.0	0.0
Property and revenue taxes	0.0	0.0	0.0
Equity in earnings of transmission affiliates	207.5	177.5	194.7
Other income, net	0.0	0.0	0.0
Interest expense	19.4	19.4	19.4
Gain on debt extinguishments	0.0	0.0
Income tax expense (benefit)	47.1	39.0	45.8
Preferred stock dividends of subsidiary	0.0	0.0	0.0
Net (income) loss attributed to noncontrolling interests	0.0	0.0	0.0
Net income (loss) attributed to common shareholders	141.0	119.1	129.5
Capital expenditures and asset acquisitions	0.0	0.0	0.0
Equity method investments	2,108.9	2,005.9	1,909.2
Total assets	$ 2,126.0	2,006.0	1,909.4
Non-Utility Energy Infrastructure
Segment information
Natural gas storage needs provided to Wisconsin utilities	33.00%
Non-Utility Energy Infrastructure | Operating segments
Segment information
Operating revenues	$ 691.3	666.5	590.0
Fuel and purchased power	0.0	0.0	0.0
Cost of natural gas sold	9.1	20.5	17.9
Other operation and maintenance	75.1	80.1	51.0
Impairment related to ICC disallowances	0.0	0.0
Depreciation and amortization	198.4	188.7	139.2
Property and revenue taxes	15.7	16.5	9.1
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Other income, net	1.0	0.0	0.0
Interest expense	99.7	94.3	68.9
Gain on debt extinguishments	0.0	0.0
Income tax expense (benefit)	(82.4)	(68.4)	(20.9)
Preferred stock dividends of subsidiary	0.0	0.0	0.0
Net (income) loss attributed to noncontrolling interests	4.1	1.2	(0.4)
Net income (loss) attributed to common shareholders	380.8	336.0	324.4
Capital expenditures and asset acquisitions	945.8	754.4	483.8
Equity method investments	0.0	0.0	0.0
Total assets	7,316.0	6,404.7	5,320.6
Corporate and other | Operating segments
Segment information
Operating revenues	0.0	0.1	0.5
Fuel and purchased power	0.0	0.0	0.0
Cost of natural gas sold	0.0	0.0	0.0
Other operation and maintenance	(11.3)	5.8	(12.9)
Impairment related to ICC disallowances	0.0	0.0
Depreciation and amortization	22.3	20.9	25.0
Property and revenue taxes	0.3	0.2	0.1
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Other income, net	54.4	53.3	14.6
Interest expense	310.0	258.1	119.4
Gain on debt extinguishments	(23.1)	(0.5)
Income tax expense (benefit)	(79.5)	(68.3)	(45.7)
Preferred stock dividends of subsidiary	0.0	0.0	0.0
Net (income) loss attributed to noncontrolling interests	0.0	0.0	0.0
Net income (loss) attributed to common shareholders	(164.3)	(162.8)	(70.8)
Capital expenditures and asset acquisitions	20.6	25.8	16.3
Equity method investments	67.0	61.3	59.1
Total assets	1,037.3	1,100.1	774.0
Public utilities
Segment information
Fuel and purchased power	1,455.7	1,615.9	1,881.4
Cost of natural gas sold	1,237.2	1,614.9	2,511.5
Other operation and maintenance	2,103.3	2,023.7	1,909.0
Impairment related to ICC disallowances	12.1	178.9
Depreciation and amortization	1,222.3	1,132.1	1,026.5
Property and revenue taxes	250.5	233.5	244.5
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Other income, net	154.5	144.9	116.5
Interest expense	748.4	705.8	643.6
Gain on debt extinguishments	0.0	0.0
Income tax expense (benefit)	336.8	302.3	343.7
Preferred stock dividends of subsidiary	1.2	1.2	1.2
Net (income) loss attributed to noncontrolling interests	0.0	0.0	0.0
Net income (loss) attributed to common shareholders	1,169.7	1,039.4	1,025.0
Capital expenditures and asset acquisitions	2,808.4	2,727.7	2,196.8
Equity method investments	15.7	14.4	13.6
Total assets	40,437.5	38,069.0	37,124.6
Public utilities | Wisconsin
Segment information
Gain on debt extinguishments		0.0
Public utilities | Wisconsin | Operating segments
Segment information
Fuel and purchased power	1,455.7	1,615.9	1,881.4
Cost of natural gas sold	661.9	894.7	1,327.4
Other operation and maintenance	1,547.9	1,531.3	1,351.3
Impairment related to ICC disallowances	0.0	0.0
Depreciation and amortization	919.9	851.5	754.7
Property and revenue taxes	169.6	179.2	182.6
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Other income, net	146.6	137.6	99.9
Interest expense	637.3	601.0	555.9
Gain on debt extinguishments	0.0
Income tax expense (benefit)	220.5	237.4	247.5
Preferred stock dividends of subsidiary	1.2	1.2	1.2
Net (income) loss attributed to noncontrolling interests	0.0	0.0	0.0
Net income (loss) attributed to common shareholders	863.1	851.3	758.4
Capital expenditures and asset acquisitions	2,347.1	2,134.4	1,610.8
Equity method investments	15.7	14.4	13.6
Total assets	30,622.7	28,527.3	27,384.0
Public utilities | Illinois
Segment information
Gain on debt extinguishments		0.0
Public utilities | Illinois | Operating segments
Segment information
Fuel and purchased power	0.0	0.0	0.0
Cost of natural gas sold	376.7	443.0	792.5
Other operation and maintenance	461.5	397.9	459.2
Impairment related to ICC disallowances	12.1	178.9
Depreciation and amortization	255.4	237.3	230.9
Property and revenue taxes	59.9	29.9	38.6
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Other income, net	7.6	6.7	14.1
Interest expense	94.7	88.9	73.8
Gain on debt extinguishments	0.0
Income tax expense (benefit)	97.6	48.6	83.1
Preferred stock dividends of subsidiary	0.0	0.0	0.0
Net (income) loss attributed to noncontrolling interests	0.0	0.0	0.0
Net income (loss) attributed to common shareholders	252.1	140.0	226.9
Capital expenditures and asset acquisitions	343.0	489.8	484.9
Equity method investments	0.0	0.0	0.0
Total assets	8,168.8	7,970.2	8,101.0
Public utilities | Other States
Segment information
Gain on debt extinguishments		0.0
Public utilities | Other States | Operating segments
Segment information
Fuel and purchased power	0.0	0.0	0.0
Cost of natural gas sold	198.6	277.2	391.6
Other operation and maintenance	93.9	94.5	98.5
Impairment related to ICC disallowances	0.0	0.0
Depreciation and amortization	47.0	43.3	40.9
Property and revenue taxes	21.0	24.4	23.3
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Other income, net	0.3	0.6	2.5
Interest expense	16.4	15.9	13.9
Gain on debt extinguishments	0.0
Income tax expense (benefit)	18.7	16.3	13.1
Preferred stock dividends of subsidiary	0.0	0.0	0.0
Net (income) loss attributed to noncontrolling interests	0.0	0.0	0.0
Net income (loss) attributed to common shareholders	54.5	48.1	39.7
Capital expenditures and asset acquisitions	118.3	103.5	101.1
Equity method investments	0.0	0.0	0.0
Total assets	1,646.0	1,571.5	1,639.6
External revenues
Segment information
Operating revenues	8,599.9	8,893.0	9,597.4
External revenues | Reconciling eliminations
Segment information
Operating revenues	0.0	0.0	0.0
External revenues | Electric transmission | Operating segments
Segment information
Operating revenues	0.0	0.0	0.0
External revenues | Non-Utility Energy Infrastructure | Operating segments
Segment information
Operating revenues	217.2	190.1	127.0
External revenues | Corporate and other | Operating segments
Segment information
Operating revenues	0.0	0.1	0.5
External revenues | Public utilities
Segment information
Operating revenues	8,382.7	8,702.8	9,469.9
External revenues | Public utilities | Wisconsin | Operating segments
Segment information
Operating revenues	6,330.5	6,625.9	6,960.5
External revenues | Public utilities | Illinois | Operating segments
Segment information
Operating revenues	1,602.4	1,557.8	1,890.9
External revenues | Public utilities | Other States | Operating segments
Segment information
Operating revenues	449.8	519.1	618.5
Intersegment revenues
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment revenues | Reconciling eliminations
Segment information
Operating revenues	(474.1)	(476.4)	(463.0)
Intersegment revenues | Electric transmission | Operating segments
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment revenues | Non-Utility Energy Infrastructure | Operating segments
Segment information
Operating revenues	474.1	476.4	463.0
Intersegment revenues | Corporate and other | Operating segments
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment revenues | Public utilities
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment revenues | Public utilities | Wisconsin | Operating segments
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment revenues | Public utilities | Illinois | Operating segments
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment revenues | Public utilities | Other States | Operating segments
Segment information
Operating revenues	$ 0.0	0.0	0.0
ATC
Segment information
Equity method investment, ownership interest (as a percent)	60.00%
Equity method investments	$ 2,085.1	1,980.8	1,884.6	$ 1,766.9
ATC | Electric transmission
Segment information
Equity method investment, ownership interest (as a percent)	60.00%
ATC Holdco
Segment information
Equity method investment, ownership interest (as a percent)	75.00%
Equity method investments	$ 23.8	$ 25.1	$ 24.6	$ 22.5
ATC Holdco | Electric transmission
Segment information
Equity method investment, ownership interest (as a percent)	75.00%