Operating Revenues - Disaggregation Of Operating Revenues by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Operating Revenues
Operating revenues	$ 8,316.0	$ 7,241.7	$ 7,523.1
Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	8,235.7	7,169.3	7,449.3
Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	80.3	72.4	73.8
Total regulated revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	8,134.2	7,093.0	7,379.1
Electric | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,516.6	4,266.1	4,307.7
Natural gas | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	3,617.6	2,826.9	3,071.4
Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	3,614.6	2,824.5	3,068.1
Other non-utility revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	101.5	76.3	70.2
Reconciling Eliminations
Disaggregation of Operating Revenues
Operating revenues	(452.8)	(448.5)	(407.4)
Reconciling Eliminations | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	(52.9)	(51.1)	(49.8)
Reconciling Eliminations | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	(399.9)	(397.4)	(357.6)
Reconciling Eliminations | Total regulated revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	(43.8)	(42.0)	(44.1)
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	(43.8)	(42.0)	(44.1)
Reconciling Eliminations | Other non-utility revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	(9.1)	(9.1)	(5.7)
Total Utility Operations
Disaggregation of Operating Revenues
Operating revenues	8,228.8	7,179.5	7,430.2
Total Utility Operations | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	79.8	71.8	37.7
Total Utility Operations | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	8,149.0	7,107.7	7,392.5
Total Utility Operations | Total regulated revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	8,131.2	7,090.6	7,375.8
Total Utility Operations | Electric | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,516.6	4,266.1	4,307.7
Total Utility Operations | Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	3,614.6	2,824.5	3,068.1
Total Utility Operations | Other non-utility revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	17.8	17.1	16.7
Wisconsin
Disaggregation of Operating Revenues
Operating revenues	6,037.0	5,473.5	5,647.1
Wisconsin | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	30.1	11.8	15.3
Wisconsin | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	6,006.9	5,461.7	5,631.8
Wisconsin | Total regulated revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	6,006.9	5,461.7	5,631.8
Wisconsin | Electric | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,516.6	4,266.1	4,307.7
Wisconsin | Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,490.3	1,195.6	1,324.1
Wisconsin | 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
Disaggregation of Operating Revenues
Operating revenues	1,672.8	1,321.9	1,357.1
Illinois | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	42.5	54.0	24.6
Illinois | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,630.3	1,267.9	1,332.5
Illinois | Total regulated revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,630.3	1,267.9	1,332.4
Illinois | 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 | Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,630.3	1,267.9	1,332.4
Illinois | 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	0.1
Other States
Disaggregation of Operating Revenues
Operating revenues	519.0	384.1	426.0
Other States | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	7.2	6.0	(2.2)
Other States | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	511.8	378.1	428.2
Other States | Total regulated revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	494.0	361.0	411.6
Other States | 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 | Natural gas | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	494.0	361.0	411.6
Other States | Other non-utility revenues | Transferred over time | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	17.8	17.1	16.6
Non-Utility Energy Infrastructure
Disaggregation of Operating Revenues
Operating revenues	539.5	508.5	495.9
Non-Utility Energy Infrastructure | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	139.6	111.0	102.6
Non-Utility Energy Infrastructure | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	399.9	397.5	393.3
Non-Utility Energy Infrastructure | Total regulated revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	46.8	44.4	47.4
Non-Utility Energy Infrastructure | 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 | Natural gas | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	46.8	44.4	47.4
Non-Utility Energy Infrastructure | Other non-utility revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	92.8	66.6	55.2
Corporate and Other
Disaggregation of Operating Revenues
Operating revenues	0.5	2.2	4.4
Corporate and Other | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.0	1.7	4.0
Corporate and Other | Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	0.5	0.5	0.4
Corporate and Other | 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 | Electric | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.0	0.0	0.0
Corporate and Other | 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 | Other non-utility revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 0.0	$ 1.7	$ 4.0