Regulatory Matters - Ohio (Details) - OHIO - PUCO - USD ($) $ in Millions					3 Months Ended	12 Months Ended
	Nov. 24, 2020	Jul. 15, 2019	Nov. 09, 2018	Jun. 01, 2016	Mar. 31, 2021	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
Regulatory Matters [Line Items]
Proposed goal to reduce CO2 pollution (percent)				90.00%
Energy Conservation, Economic Development and Job Retention
Regulatory Matters [Line Items]
Contribution amount				$ 51.0
Distribution Modernization Rider
Regulatory Matters [Line Items]
Annual revenue cap for rider							$ 132.5
Recovery period							3 years
Approved amount for rider						$ 168.0	$ 168.0
Requested plan extension period	2 years
Delivery Capital Recovery Rider
Regulatory Matters [Line Items]
Annual revenue cap for rider for years three through six				20.0
Annual revenue cap for rider for years six through eight				$ 15.0
OCC DMR Refund | The Ohio Companies
Regulatory Matters [Line Items]
Loss contingency, damages sought		$ 42.0
Distribution Platform Modernization Plan
Regulatory Matters [Line Items]
Approved amount of annual increase (decrease)			$ 516.0
Period of grid modernization plan			3 years
Decoupling Rider | The Ohio Companies
Regulatory Matters [Line Items]
Amount of refunds announced					$ 27.0
Rider CSR | The Ohio Companies
Regulatory Matters [Line Items]
Pre-tax impairment of regulatory asset								$ 108.0
Impairment of regulatory asset, net								84.0
Lost distribution revenue								$ 77.0