Regulatory Matters - Ohio (Details) $ in Millions							6 Months Ended
	Apr. 25, 2018 USD ($)	Mar. 12, 2018	Dec. 01, 2017 USD ($)	Oct. 12, 2016 USD ($)	Apr. 15, 2016	Aug. 07, 2013 USD ($) auction	Jun. 30, 2018 USD ($)	Feb. 15, 2018 USD ($)
Regulatory Matters [Line Items]
Proposed goal to reduce CO2 pollution (percent)							90.00%
Ohio
Regulatory Matters [Line Items]
Energy efficient portfolio plan term					3 years
Estimated cost of plans							$ 268.0
Credit to non-shopping customers						$ 43.4
Ohio | PUCO
Regulatory Matters [Line Items]
Proposed goal to reduce CO2 pollution (percent)				90.00%
Requested removal of cost cap		4.00%
Number of renewable energy auctions | auction						1
Reversal of reserve	$ 72.0
Interest on reversal	$ 29.0
Ohio | Distribution Modernization Rider
Regulatory Matters [Line Items]
Amount of rider valuation				$ 558.0
Period of rider valuation				8 years
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
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
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