Operating Revenues - Disaggregation Of Operating Revenues by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Operating Revenues
Operating revenues	$ 8,893.0	$ 9,597.4	$ 8,316.0
Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	8,785.3	9,568.1	8,235.7
Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	107.7	29.3	80.3
Total regulated revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	8,577.2	9,424.9	8,134.2
Electric | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,994.6	4,956.2	4,516.6
Natural gas | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	3,582.6	4,468.7	3,617.6
Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	3,580.9	4,466.2	3,614.6
Other non-utility revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	208.1	143.2	101.5
Reconciling Eliminations
Disaggregation of Operating Revenues
Operating revenues	(476.4)	(463.0)	(452.8)
Reconciling Eliminations | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	(69.3)	(60.9)	(52.9)
Reconciling Eliminations | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	(407.1)	(402.1)	(399.9)
Reconciling Eliminations | Total regulated revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	(60.2)	(51.8)	(43.8)
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	(60.2)	(51.8)	(43.8)
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	8,702.8	9,469.9	8,228.8
Total Utility Operations | Operating segments | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	107.7	28.8	79.8
Total Utility Operations | Operating segments | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	8,595.1	9,441.1	8,149.0
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	8,575.5	9,422.4	8,131.2
Total Utility Operations | Operating segments | Electric | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,994.6	4,956.2	4,516.6
Total Utility Operations | Operating segments | Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	3,580.9	4,466.2	3,614.6
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	19.6	18.7	17.8
Wisconsin | Electric | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,994.6	4,956.2	4,516.6
Wisconsin | Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,606.7	1,980.7	1,490.3
Wisconsin | Operating segments
Disaggregation of Operating Revenues
Operating revenues	6,625.9	6,960.5	6,037.0
Wisconsin | Operating segments | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	24.6	23.6	30.1
Wisconsin | Operating segments | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	6,601.3	6,936.9	6,006.9
Wisconsin | Operating segments | Total regulated revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	6,601.3	6,936.9	6,006.9
Wisconsin | Operating segments | Electric | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,994.6	4,956.2	4,516.6
Wisconsin | Operating segments | Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,606.7	1,980.7	1,490.3
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	1,480.5	1,883.7	1,630.3
Illinois | Operating segments
Disaggregation of Operating Revenues
Operating revenues	1,557.8	1,890.9	1,672.8
Illinois | Operating segments | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	77.3	7.2	42.5
Illinois | Operating segments | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,480.5	1,883.7	1,630.3
Illinois | Operating segments | Total regulated revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,480.5	1,883.7	1,630.3
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	1,480.5	1,883.7	1,630.3
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	493.7	601.8	494.0
Other States | Operating segments
Disaggregation of Operating Revenues
Operating revenues	519.1	618.5	519.0
Other States | Operating segments | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	5.8	(2.0)	7.2
Other States | Operating segments | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	513.3	620.5	511.8
Other States | Operating segments | Total regulated revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	493.7	601.8	494.0
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	493.7	601.8	494.0
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	19.6	18.7	17.8
Non-Utility Energy Infrastructure | Operating segments
Disaggregation of Operating Revenues
Operating revenues	666.5	590.0	539.5
Non-Utility Energy Infrastructure | Operating segments | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	259.4	187.9	139.6
Non-Utility Energy Infrastructure | Operating segments | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	407.1	402.1	399.9
Non-Utility Energy Infrastructure | Operating segments | Total regulated revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	61.9	54.3	46.8
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	61.9	54.3	46.8
Non-Utility Energy Infrastructure | Operating segments | Other non-utility revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	197.5	133.6	92.8
Corporate and Other | Operating segments
Disaggregation of Operating Revenues
Operating revenues	0.1	0.5	0.5
Corporate and Other | Operating segments | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.1	0.0	0.0
Corporate and Other | Operating segments | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	0.0	0.5	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	$ 0.1	$ 0.0	$ 0.0