Regulatory Matters - Ohio (Details) - USD ($) $ in Millions									9 Months Ended	12 Months Ended
	Oct. 09, 2019	Oct. 01, 2019	Apr. 19, 2019	Mar. 29, 2019	Nov. 09, 2018	Mar. 12, 2018	Dec. 01, 2017	Jun. 01, 2016	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017	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
Approved amount for rider										$ 168.0
OHIO | Distribution Modernization Rider | PUCO | Subsequent Event
Regulatory Matters [Line Items]
Approved amount of annual increase (decrease)		$ (28.0)
OHIO | Delivery Capital Recovery Rider | PUCO
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
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 | Regional Transmission Expansion Plan | PUCO | Subsequent Event
Regulatory Matters [Line Items]
Approved amount of annual increase (decrease)	$ 95.0
The Ohio Companies | OHIO | OCC DMR Refund | PUCO
Regulatory Matters [Line Items]
Loss contingency, damages sought			$ 42.0