Operating Revenues - Disaggregation Of Operating Revenues by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Disaggregation of Operating Revenues
Operating revenues	$ 8,599.9	$ 8,893.0	$ 9,597.4
Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	8,467.7	8,785.3	9,568.1
Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	132.2	107.7	29.3
Total regulated revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	8,232.5	8,577.2	9,424.9
Electric | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,908.4	4,994.6	4,956.2
Natural gas | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	3,324.1	3,582.6	4,468.7
Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	3,321.7	3,580.9	4,466.2
Other non-utility revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	235.2	208.1	143.2
Reconciling Eliminations
Disaggregation of Operating Revenues
Operating revenues	(474.1)	(476.4)	(463.0)
Reconciling Eliminations | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	(55.1)	(69.3)	(60.9)
Reconciling Eliminations | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	(419.0)	(407.1)	(402.1)
Reconciling Eliminations | Total regulated revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	(46.0)	(60.2)	(51.8)
Reconciling Eliminations | Electric | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.0	0.0	0.0
Reconciling Eliminations | Natural gas | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	(46.0)	(60.2)	(51.8)
Reconciling Eliminations | Other non-utility revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	(9.1)	(9.1)	(9.1)
Total Utility Operations | Operating segments
Disaggregation of Operating Revenues
Operating revenues	8,382.7	8,702.8	9,469.9
Total Utility Operations | Operating segments | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	132.2	107.7	28.8
Total Utility Operations | Operating segments | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	8,250.5	8,595.1	9,441.1
Total Utility Operations | Operating segments | Total regulated revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	8,230.1	8,575.5	9,422.4
Total Utility Operations | Operating segments | Electric | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,908.4	4,994.6	4,956.2
Total Utility Operations | Operating segments | Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	3,321.7	3,580.9	4,466.2
Total Utility Operations | Operating segments | Other non-utility revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	20.4	19.6	18.7
Wisconsin | Electric | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,908.4	4,994.6	4,956.2
Wisconsin | Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,402.4	1,606.7	1,980.7
Wisconsin | Operating segments
Disaggregation of Operating Revenues
Operating revenues	6,330.5	6,625.9	6,960.5
Wisconsin | Operating segments | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	19.7	24.6	23.6
Wisconsin | Operating segments | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	6,310.8	6,601.3	6,936.9
Wisconsin | Operating segments | Total regulated revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	6,310.8	6,601.3	6,936.9
Wisconsin | Operating segments | Electric | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,908.4	4,994.6	4,956.2
Wisconsin | Operating segments | Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,402.4	1,606.7	1,980.7
Wisconsin | Operating segments | Other non-utility revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.0	0.0	0.0
Illinois | Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,499.6	1,480.5	1,883.7
Illinois | Operating segments
Disaggregation of Operating Revenues
Operating revenues	1,602.4	1,557.8	1,890.9
Illinois | Operating segments | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	102.8	77.3	7.2
Illinois | Operating segments | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,499.6	1,480.5	1,883.7
Illinois | Operating segments | Total regulated revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,499.6	1,480.5	1,883.7
Illinois | Operating segments | Electric | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.0	0.0	0.0
Illinois | Operating segments | Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,499.6	1,480.5	1,883.7
Illinois | Operating segments | Other non-utility revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.0	0.0	0.0
Other States | Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	419.7	493.7	601.8
Other States | Operating segments
Disaggregation of Operating Revenues
Operating revenues	449.8	519.1	618.5
Other States | Operating segments | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	9.7	5.8	(2.0)
Other States | Operating segments | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	440.1	513.3	620.5
Other States | Operating segments | Total regulated revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	419.7	493.7	601.8
Other States | Operating segments | Electric | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.0	0.0	0.0
Other States | Operating segments | Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	419.7	493.7	601.8
Other States | Operating segments | Other non-utility revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	20.4	19.6	18.7
Non-Utility Energy Infrastructure | Operating segments
Disaggregation of Operating Revenues
Operating revenues	691.3	666.5	590.0
Non-Utility Energy Infrastructure | Operating segments | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	272.3	259.4	187.9
Non-Utility Energy Infrastructure | Operating segments | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	419.0	407.1	402.1
Non-Utility Energy Infrastructure | Operating segments | Total regulated revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	48.4	61.9	54.3
Non-Utility Energy Infrastructure | Operating segments | Electric | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.0	0.0	0.0
Non-Utility Energy Infrastructure | Operating segments | Natural gas | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	48.4	61.9	54.3
Non-Utility Energy Infrastructure | Operating segments | Other non-utility revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	223.9	197.5	133.6
Corporate and Other | Operating segments
Disaggregation of Operating Revenues
Operating revenues	0.0	0.1	0.5
Corporate and Other | Operating segments | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.0	0.1	0.0
Corporate and Other | Operating segments | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	0.0	0.0	0.5
Corporate and Other | Operating segments | Total regulated revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.0	0.0	0.0
Corporate and Other | Operating segments | Electric | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.0	0.0	0.0
Corporate and Other | Operating segments | Natural gas | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.0	0.0	0.0
Corporate and Other | Operating segments | Other non-utility revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 0.0	$ 0.1	$ 0.0