Segment Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) numberOfSegments	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Segment information
Number of reportable segments | numberOfSegments	6
Operating revenues	$ 8,893.0	$ 9,597.4	$ 8,316.0
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
Equity in earnings of transmission affiliates	177.5	194.7	158.1
Interest expense	726.9	515.1	471.1
Loss on debt extinguishment	0.0	0.0	36.3
Income tax expense (benefit)	204.6	322.9	200.3
Net income (loss)	1,331.7	1,409.7	1,298.5
Net income (loss) attributed to common shareholders	1,331.7	1,408.1	1,300.3
Capital expenditures and asset acquisitions	3,507.9	2,696.9	2,372.7
Total assets	43,939.7	41,872.1	38,988.5
Reconciling eliminations
Segment information
Other operation and maintenance	(9.1)	(9.1)	(9.2)
Impairment related to ICC disallowances	0.0
Depreciation and amortization	(77.5)	(68.1)	(60.0)
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Interest expense	(350.2)	(336.2)	(340.5)
Loss on debt extinguishment			0.0
Income tax expense (benefit)	0.0	0.0	0.0
Net income (loss)	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
Total assets	(3,640.1)	(3,256.5)	(3,264.6)
Reconciling eliminations | WE
Segment information
Total assets	1,630.6	1,632.9	1,729.9
Wisconsin | Operating segments
Segment information
Operating revenues	6,625.9	6,960.5	6,037.0
Illinois | Operating segments
Segment information
Operating revenues	1,557.8	1,890.9	1,672.8
Other States | Operating segments
Segment information
Operating revenues	519.1	618.5	519.0
Electric transmission | Operating segments
Segment information
Other operation and maintenance	0.0	0.0	0.0
Impairment related to ICC disallowances	0.0
Depreciation and amortization	0.0	0.0	0.0
Equity in earnings of transmission affiliates	177.5	194.7	158.1
Interest expense	19.4	19.4	19.4
Loss on debt extinguishment			0.0
Income tax expense (benefit)	39.0	45.8	32.3
Net income (loss)	119.1	129.5	106.3
Net income (loss) attributed to common shareholders	119.1	129.5	106.3
Capital expenditures and asset acquisitions	0.0	0.0	0.0
Total assets	$ 2,006.0	1,909.4	1,792.7
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	$ 666.5	590.0	539.5
Other operation and maintenance	80.1	51.0	43.1
Impairment related to ICC disallowances	0.0
Depreciation and amortization	188.7	139.2	125.3
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Interest expense	94.3	68.9	71.0
Loss on debt extinguishment			0.0
Income tax expense (benefit)	(68.4)	(20.9)	3.1
Net income (loss)	334.8	324.8	276.2
Net income (loss) attributed to common shareholders	336.0	324.4	279.2
Capital expenditures and asset acquisitions	754.4	483.8	335.3
Total assets	6,404.7	5,320.6	4,627.7
Corporate and other | Operating segments
Segment information
Operating revenues	0.1	0.5	0.5
Other operation and maintenance	5.8	(12.9)	(7.5)
Impairment related to ICC disallowances	0.0
Depreciation and amortization	20.9	25.0	25.9
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Interest expense	257.6	119.4	92.8
Loss on debt extinguishment			36.3
Income tax expense (benefit)	(68.3)	(45.7)	(45.8)
Net income (loss)	(162.8)	(70.8)	(50.5)
Net income (loss) attributed to common shareholders	(162.8)	(70.8)	(50.5)
Capital expenditures and asset acquisitions	25.8	16.3	18.1
Total assets	1,100.1	774.0	785.3
Public utilities
Segment information
Other operation and maintenance	2,023.7	1,909.0	1,979.1
Impairment related to ICC disallowances	178.9
Depreciation and amortization	1,132.1	1,026.5	983.1
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Interest expense	705.8	643.6	628.4
Loss on debt extinguishment			0.0
Income tax expense (benefit)	302.3	343.7	210.7
Net income (loss)	1,040.6	1,026.2	966.5
Net income (loss) attributed to common shareholders	1,039.4	1,025.0	965.3
Capital expenditures and asset acquisitions	2,727.7	2,196.8	2,019.3
Total assets	38,069.0	37,124.6	35,047.4
Public utilities | Wisconsin | Operating segments
Segment information
Other operation and maintenance	1,531.3	1,351.3	1,455.2
Impairment related to ICC disallowances	0.0
Depreciation and amortization	851.5	754.7	726.9
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Interest expense	601.0	555.9	555.6
Loss on debt extinguishment			0.0
Income tax expense (benefit)	237.4	247.5	119.9
Net income (loss)	852.5	759.6	707.7
Net income (loss) attributed to common shareholders	851.3	758.4	706.5
Capital expenditures and asset acquisitions	2,134.4	1,610.8	1,389.7
Total assets	28,527.3	27,384.0	25,687.9
Public utilities | Illinois | Operating segments
Segment information
Other operation and maintenance	397.9	459.2	433.5
Impairment related to ICC disallowances	178.9
Depreciation and amortization	237.3	230.9	218.1
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Interest expense	88.9	73.8	66.6
Loss on debt extinguishment			0.0
Income tax expense (benefit)	48.6	83.1	79.3
Net income (loss)	140.0	226.9	223.0
Net income (loss) attributed to common shareholders	140.0	226.9	223.0
Capital expenditures and asset acquisitions	489.8	484.9	533.7
Total assets	7,970.2	8,101.0	7,853.4
Public utilities | Other States | Operating segments
Segment information
Other operation and maintenance	94.5	98.5	90.4
Impairment related to ICC disallowances	0.0
Depreciation and amortization	43.3	40.9	38.1
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Interest expense	15.9	13.9	6.2
Loss on debt extinguishment			0.0
Income tax expense (benefit)	16.3	13.1	11.5
Net income (loss)	48.1	39.7	35.8
Net income (loss) attributed to common shareholders	48.1	39.7	35.8
Capital expenditures and asset acquisitions	103.5	101.1	95.9
Total assets	1,571.5	1,639.6	1,506.1
External revenues
Segment information
Operating revenues	8,893.0	9,597.4	8,316.0
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	190.1	127.0	86.7
External revenues | Corporate and other | Operating segments
Segment information
Operating revenues	0.1	0.5	0.5
External revenues | Public utilities
Segment information
Operating revenues	8,702.8	9,469.9	8,228.8
External revenues | Public utilities | Wisconsin | Operating segments
Segment information
Operating revenues	6,625.9	6,960.5	6,037.0
External revenues | Public utilities | Illinois | Operating segments
Segment information
Operating revenues	1,557.8	1,890.9	1,672.8
External revenues | Public utilities | Other States | Operating segments
Segment information
Operating revenues	519.1	618.5	519.0
Intersegment transactions
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment transactions | Reconciling eliminations
Segment information
Operating revenues	(476.4)	(463.0)	(452.8)
Intersegment transactions | Electric transmission | Operating segments
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment transactions | Non-Utility Energy Infrastructure | Operating segments
Segment information
Operating revenues	476.4	463.0	452.8
Intersegment transactions | Corporate and other | Operating segments
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment transactions | Public utilities
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment transactions | Public utilities | Wisconsin | Operating segments
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment transactions | Public utilities | Illinois | Operating segments
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment transactions | 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%
Other operation and maintenance	$ 377.5	$ 363.7	$ 361.0
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%
ATC Holdco | Electric transmission
Segment information
Equity method investment, ownership interest (as a percent)	75.00%