Regulatory Matters - Ohio (Details) - USD ($) $ in Millions							3 Months Ended
	Mar. 29, 2019	Feb. 01, 2019	Nov. 09, 2018	Mar. 12, 2018	Dec. 01, 2017	Oct. 12, 2016	Mar. 31, 2019	Feb. 15, 2018
Regulatory Matters [Line Items]
Proposed goal to reduce CO2 pollution (percent)							90.00%
OHIO
Regulatory Matters [Line Items]
Estimated cost of plans							$ 268.0
OHIO | PUCO
Regulatory Matters [Line Items]
Proposed goal to reduce CO2 pollution (percent)						90.00%
Requested removal of cost cap				4.00%
OHIO | Distribution Modernization Rider | PUCO
Regulatory Matters [Line Items]
Annual revenue cap for rider						$ 132.5
Recovery period						3 years
Possible extension period						2 years
Approved amount for rider						$ 168.0
Excessive earnings test exclusion period						3 years
Renewal period for excessive earnings test exclusion period		2 years				2 years
OHIO | Delivery Capital Recovery Rider | PUCO
Regulatory Matters [Line Items]
Annual revenue cap for rider						$ 30.0
Annual revenue cap for rider for years three through six						20.0
Annual revenue cap for rider for years six through eight						15.0
OHIO | Distribution Platform Modernization Plan | PUCO
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)					$ 450.0
Approved amount of annual increase (decrease)			$ 516.0
Period of grid modernization plan			3 years
OHIO | Energy Conservation, Economic Development and Job Retention | PUCO
Regulatory Matters [Line Items]
Contribution amount						$ 51.0
The Ohio Companies | OHIO | PUCO
Regulatory Matters [Line Items]
Impact on base rate								$ 40.0
The Ohio Companies | OHIO | Regional Transmission Expansion Plan | PUCO
Regulatory Matters [Line Items]
Amount excluded from approved rate recovery	$ 95.0