Commitments and Contingencies - Environmental Matters (Details) T in Millions, $ in Millions	1 Months Ended	12 Months Ended		15 Months Ended
	Oct. 31, 2020 States	Dec. 31, 2020 USD ($) performance_obligations T MW	Dec. 31, 2019 USD ($)	Mar. 31, 2019 MW
Climate Change | Electric
Air Quality
No other source category, except for EGUs, should contribute to GHG emissions above this percentage threshold		3.00%
Company goal met in 2019 for percentage of carbon dioxide emissions reductions by 2030			40.00%
Company goal for percentage of carbon dioxide emissions reduction below 2005 levels by 2030		70.00%
Company near-term goal for percentage carbon dioxide emission reduction goal by 2025		55.00%
Capacity of coal generation retired since the beginning of 2018, in megawatts | MW				1,800
Capacity of fossil-fueled generation to be retired by 2025, in megawatts | MW		1,800
Per mile rate of methane emission reduction		30.00%
Carbon dioxide emissions | T		20.1
Climate Change | Natural gas
Air Quality
Carbon dioxide emissions | T		27.4
Cross State Air Pollution Rule Update Rule Revision | Electric
Air Quality
Number of states in group 2 for CSAPR update rule revision | States	9
Number of states affected by the CSAPR update rule revision | States	21
Steam Electric Effluent Guidelines | Electric
Water Quality
Number of new ELG rule requirements that affect our electric utilities | performance_obligations		2
Expected capital investment to achieve required discharge limits		$ 110.0
Manufactured Gas Plant Remediation | Natural gas
Manufactured Gas Plant Remediation
Regulatory assets recorded for remediation of manufactured gas plant sites		638.2	$ 685.5
Reserves for future environmental remediation of manufactured gas plant sites		$ 532.9	$ 589.2
Renewables, Efficiency, and Conservation | Electric | Wisconsin
Renewables, Efficiency, and Conservation
Annual state renewable portfolio requirement, as a percent		10.00%
Percent of annual operating revenues used to fund renewable program		1.20%
Renewables, Efficiency, and Conservation | Electric | Wisconsin | WE
Renewables, Efficiency, and Conservation
Required renewable energy percent achieved		8.27%
Renewables, Efficiency, and Conservation | Electric | Wisconsin | WPS
Renewables, Efficiency, and Conservation
Required renewable energy percent achieved		9.74%
Renewables, Efficiency, and Conservation | Electric | Michigan
Renewables, Efficiency, and Conservation
Annual state renewable portfolio requirement for 2019 and 2020, as a percent		12.50%
Energy optimization target, as a percent		1.00%
State renewable portfolio requirement for 2021, as a percent		15.00%