Regulatory Matters - Ohio (Details) - USD ($) $ in Millions								6 Months Ended
	Apr. 19, 2019	Mar. 29, 2019	Feb. 01, 2019	Nov. 09, 2018	Mar. 12, 2018	Dec. 01, 2017	Oct. 12, 2016	Jun. 30, 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
The Ohio Companies | OHIO | OCC DMR Refund | PUCO
Regulatory Matters [Line Items]
Loss contingency, damages sought	$ 42.0