Operating Revenues - Disaggregation of Natural Gas Utility Operating Revenues by Customer Class (Details) - Revenues from contracts with customers - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 9,568.1	$ 8,235.7	$ 7,169.3
Natural gas
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,468.7	3,617.6	2,826.9
Natural gas | Transferred over time
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,466.2	3,614.6	2,824.5
Natural gas | Transferred over time | Total retail revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,222.9	3,092.1	2,450.5
Natural gas | Transferred over time | Residential
Disaggregation of Operating Revenues
Revenues from contracts with customers	2,922.7	2,188.0	1,775.6
Natural gas | Transferred over time | Commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,300.2	904.1	674.9
Natural gas | Transferred over time | Transport
Disaggregation of Operating Revenues
Revenues from contracts with customers	376.1	343.0	326.2
Natural gas | Transferred over time | Other utility revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	(132.8)	179.5	47.8
Wisconsin | Transferred over time
Disaggregation of Operating Revenues
Revenues from contracts with customers	6,936.9	6,006.9	5,461.7
Wisconsin | Natural gas | Transferred over time
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,980.7	1,490.3	1,195.6
Wisconsin | Natural gas | Transferred over time | Total retail revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,906.7	1,401.0	1,090.7
Wisconsin | Natural gas | Transferred over time | Residential
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,234.0	928.9	752.6
Wisconsin | Natural gas | Transferred over time | Commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	672.7	472.1	338.1
Wisconsin | Natural gas | Transferred over time | Transport
Disaggregation of Operating Revenues
Revenues from contracts with customers	81.8	80.0	79.1
Wisconsin | Natural gas | Transferred over time | Other utility revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	(7.8)	9.3	25.8
Illinois | Transferred over time
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,883.7	1,630.3	1,267.9
Illinois | Natural gas | Transferred over time
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,883.7	1,630.3	1,267.9
Illinois | Natural gas | Transferred over time | Total retail revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,706.2	1,320.0	1,023.2
Illinois | Natural gas | Transferred over time | Residential
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,297.4	1,017.9	802.2
Illinois | Natural gas | Transferred over time | Commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	408.8	302.1	221.0
Illinois | Natural gas | Transferred over time | Transport
Disaggregation of Operating Revenues
Revenues from contracts with customers	259.8	231.2	215.6
Illinois | Natural gas | Transferred over time | Other utility revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	(82.3)	79.1	29.1
Other States | Transferred over time
Disaggregation of Operating Revenues
Revenues from contracts with customers	620.5	511.8	378.1
Other States | Natural gas | Transferred over time
Disaggregation of Operating Revenues
Revenues from contracts with customers	601.8	494.0	361.0
Other States | Natural gas | Transferred over time | Total retail revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	610.0	371.1	336.6
Other States | Natural gas | Transferred over time | Residential
Disaggregation of Operating Revenues
Revenues from contracts with customers	391.3	241.2	220.8
Other States | Natural gas | Transferred over time | Commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	218.7	129.9	115.8
Other States | Natural gas | Transferred over time | Transport
Disaggregation of Operating Revenues
Revenues from contracts with customers	34.5	31.8	31.5
Other States | Natural gas | Transferred over time | Other utility revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ (42.7)	$ 91.1	$ (7.1)