Segment Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) segment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Segment information
Number of reportable segments | segment	6
Operating revenues	$ 9,597.4	$ 8,316.0	$ 7,241.7
Other operation and maintenance	1,938.0	2,005.5	2,032.2
Depreciation and amortization	1,122.6	1,074.3	975.9
Equity in earnings of transmission affiliates	194.7	158.1	175.8
Interest expense	515.1	471.1	493.7
Loss on debt extinguishment	0.0	36.3	38.4
Income tax expense (benefit)	322.9	200.3	227.9
Net income (loss)	1,409.7	1,298.5	1,201.4
Net income (loss) attributed to common shareholders	1,408.1	1,300.3	1,199.9
Capital expenditures and asset acquisitions	2,696.9	2,372.7	2,874.3
Total assets	41,872.1	38,988.5	37,028.1
Reconciling eliminations
Segment information
Other operation and maintenance	(9.1)	(9.2)	(9.2)
Depreciation and amortization	(68.1)	(60.0)	(52.8)
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Interest expense	(336.2)	(340.5)	(345.5)
Loss on debt extinguishment		0.0	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	(3,256.5)	(3,264.6)	(3,361.2)
Reconciling eliminations | WE
Segment information
Total assets	1,632.9	1,729.9	1,824.5
Wisconsin
Segment information
Operating revenues	6,960.5	6,037.0	5,473.5
Illinois
Segment information
Operating revenues	1,890.9	1,672.8	1,321.9
Other States
Segment information
Operating revenues	618.5	519.0	384.1
Electric transmission
Segment information
Other operation and maintenance	0.0	0.0	0.0
Depreciation and amortization	0.0	0.0	0.0
Equity in earnings of transmission affiliates	194.7	158.1	175.8
Interest expense	19.4	19.4	19.4
Loss on debt extinguishment		0.0	0.0
Income tax expense (benefit)	45.8	32.3	43.7
Net income (loss)	129.5	106.3	112.6
Net income (loss) attributed to common shareholders	129.5	106.3	112.6
Capital expenditures and asset acquisitions	0.0	0.0	0.0
Total assets	$ 1,909.4	1,792.7	1,764.7
Non-Utility Energy Infrastructure
Segment information
Natural gas storage needs provided to Wisconsin utilities	33.00%
Operating revenues	$ 590.0	539.5	508.5
Other operation and maintenance	51.0	43.1	24.9
Depreciation and amortization	139.2	125.3	98.9
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Interest expense	68.9	71.0	60.8
Loss on debt extinguishment		0.0	0.0
Income tax expense (benefit)	(20.9)	3.1	44.7
Net income (loss)	324.8	276.2	261.1
Net income (loss) attributed to common shareholders	324.4	279.2	260.8
Capital expenditures and asset acquisitions	483.8	335.3	661.8
Total assets	5,320.6	4,627.7	4,455.2
Corporate and other
Segment information
Operating revenues	0.5	0.5	2.2
Other operation and maintenance	(12.9)	(7.5)	17.4
Depreciation and amortization	25.0	25.9	25.1
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Interest expense	119.4	92.8	124.0
Loss on debt extinguishment		36.3	38.4
Income tax expense (benefit)	(45.7)	(45.8)	(72.4)
Net income (loss)	(70.8)	(50.5)	(106.4)
Net income (loss) attributed to common shareholders	(70.8)	(50.5)	(106.4)
Capital expenditures and asset acquisitions	16.3	18.1	33.1
Total assets	774.0	785.3	762.2
Public utilities
Segment information
Other operation and maintenance	1,909.0	1,979.1	1,999.1
Depreciation and amortization	1,026.5	983.1	904.7
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Interest expense	643.6	628.4	635.0
Loss on debt extinguishment		0.0	0.0
Income tax expense (benefit)	343.7	210.7	211.9
Net income (loss)	1,026.2	966.5	934.1
Net income (loss) attributed to common shareholders	1,025.0	965.3	932.9
Capital expenditures and asset acquisitions	2,196.8	2,019.3	2,179.4
Total assets	37,124.6	35,047.4	33,407.2
Public utilities | Wisconsin
Segment information
Other operation and maintenance	1,351.3	1,455.2	1,476.7
Depreciation and amortization	754.7	726.9	674.5
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Interest expense	555.9	555.6	561.3
Loss on debt extinguishment		0.0	0.0
Income tax expense (benefit)	247.5	119.9	132.7
Net income (loss)	759.6	707.7	691.6
Net income (loss) attributed to common shareholders	758.4	706.5	690.4
Capital expenditures and asset acquisitions	1,610.8	1,389.7	1,382.4
Total assets	27,384.0	25,687.9	24,599.2
Public utilities | Illinois
Segment information
Other operation and maintenance	459.2	433.5	435.4
Depreciation and amortization	230.9	218.1	196.7
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Interest expense	73.8	66.6	63.5
Loss on debt extinguishment		0.0	0.0
Income tax expense (benefit)	83.1	79.3	66.1
Net income (loss)	226.9	223.0	203.5
Net income (loss) attributed to common shareholders	226.9	223.0	203.5
Capital expenditures and asset acquisitions	484.9	533.7	652.7
Total assets	8,101.0	7,853.4	7,471.8
Public utilities | Other States
Segment information
Other operation and maintenance	98.5	90.4	87.0
Depreciation and amortization	40.9	38.1	33.5
Equity in earnings of transmission affiliates	0.0	0.0	0.0
Interest expense	13.9	6.2	10.2
Loss on debt extinguishment		0.0	0.0
Income tax expense (benefit)	13.1	11.5	13.1
Net income (loss)	39.7	35.8	39.0
Net income (loss) attributed to common shareholders	39.7	35.8	39.0
Capital expenditures and asset acquisitions	101.1	95.9	144.3
Total assets	1,639.6	1,506.1	1,336.2
External revenues
Segment information
Operating revenues	9,597.4	8,316.0	7,241.7
External revenues | Reconciling eliminations
Segment information
Operating revenues	0.0	0.0	0.0
External revenues | Electric transmission
Segment information
Operating revenues	0.0	0.0	0.0
External revenues | Non-Utility Energy Infrastructure
Segment information
Operating revenues	127.0	86.7	60.0
External revenues | Corporate and other
Segment information
Operating revenues	0.5	0.5	2.2
External revenues | Public utilities
Segment information
Operating revenues	9,469.9	8,228.8	7,179.5
External revenues | Public utilities | Wisconsin
Segment information
Operating revenues	6,960.5	6,037.0	5,473.5
External revenues | Public utilities | Illinois
Segment information
Operating revenues	1,890.9	1,672.8	1,321.9
External revenues | Public utilities | Other States
Segment information
Operating revenues	618.5	519.0	384.1
Intersegment transactions
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment transactions | Reconciling eliminations
Segment information
Operating revenues	(463.0)	(452.8)	(448.5)
Intersegment transactions | Electric transmission
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment transactions | Non-Utility Energy Infrastructure
Segment information
Operating revenues	463.0	452.8	448.5
Intersegment transactions | Corporate and other
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
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment transactions | Public utilities | Illinois
Segment information
Operating revenues	0.0	0.0	0.0
Intersegment transactions | Public utilities | Other States
Segment information
Operating revenues	$ 0.0	$ 0.0	$ 0.0
ATC
Segment information
Equity method investment, ownership interest (as a percent)	60.00%
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%