Acquisitions, Investments and Dispositions - Pilesgrove (Details) $ in Millions	1 Months Ended
	Aug. 31, 2016 USD ($)	Jun. 30, 2016 USD ($) MW	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Pilesgrove
Business Acquisition [Line Items]
Generating capacity (MW AC) | MW		18
Net assets			$ 45	$ 45
Con Edison Development | Pilesgrove
Business Acquisition [Line Items]
Percentage of voting interest acquired	50.00%
Purchase price	$ 16
Bargain purchase gain	8
Bargain purchase gain, net of taxes	5
Non-utility property	45
Other current assets	$ 3
Con Edison Development | Pilesgrove
Business Acquisition [Line Items]
Equity method investment, impairment charge		$ 8
Equity method investment, impairment charge, net of taxes		$ 5
Percentage of equity interest owned		50.00%