Regulatory Matters - Ohio (Details) - Ohio $ in Millions			9 Months Ended	12 Months Ended
	Aug. 07, 2013 USD ($) auction	Mar. 20, 2013	Sep. 30, 2015 MWh	Dec. 31, 2015 USD ($) MW
Regulatory Matters [Line Items]
ESP extension term				2 years
Generation discount for low income customers				6.00%
Recovery period				5 years
Costs avoided by customers				$ 360.0
Generation supply auction period, after approval				3 years
EDA plan term				3 years
Proposed purchase power agreement term				8 years
EEPP term of plan		3 years
Generation supply auction period, before approval				1 year
Portfolio plan estimated cost				$ 250.0
Portion of revenue obtained to be received				20.00%
Credit to non-shopping customers	$ 43.4
Year 2015
Regulatory Matters [Line Items]
Annual energy savings | MWh			2,266
Year 2016
Regulatory Matters [Line Items]
Annual energy savings | MWh			2,288
Year 2017
Regulatory Matters [Line Items]
Annual energy savings yearly increase (percent)				1.00%
Annually Through 2018
Regulatory Matters [Line Items]
Utilities required to additionally reduce peak demand				0.75%
Annually Through 2014
Regulatory Matters [Line Items]
Utilities required to additionally reduce peak demand				0.75%
Wind or Solar Power
Regulatory Matters [Line Items]
Proposed potential plant acquisition | MW				100
DCR Rider
Regulatory Matters [Line Items]
Annual revenue cap for rider				$ 30.0
Revenue cap for Rider for years 3-6				20.0
Revenue cap for Rider for years 6-8				15.0
RRS Rider
Regulatory Matters [Line Items]
Guaranteed credits in year five				10.0
Guaranteed credits in year six				20.0
Guaranteed credits in year seven				30.0
Guaranteed credits in year eight				$ 40.0
Number of renewable energy auctions | auction	1
Customary Advisory Council
Regulatory Matters [Line Items]
Proposed purchase power agreement term				8 years
Public Utilities, Annual Contribution Amount				$ 1.0
Public Utilities, Contribution Amount				$ 8.0
Ohio Companies | Energy Conservation, Economic Development and Job Retention
Regulatory Matters [Line Items]
Proposed purchase power agreement term				8 years
Public Utilities, Annual Contribution Amount				$ 3.0
Public Utilities, Contribution Amount				$ 24.0
Ohio Companies | Fuel-Fund
Regulatory Matters [Line Items]
Proposed purchase power agreement term				8 years
Public Utilities, Annual Contribution Amount				$ 2.4
Public Utilities, Contribution Amount				$ 19.0