Acquisitions, Investments and Dispositions - NY Transco (Details) - USD ($) $ in Millions	1 Months Ended
	May 31, 2016	Dec. 31, 2016	Jan. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Equity method investment		$ 488		$ 574
CET Electric
Schedule of Equity Method Investments [Line Items]
Ownership interest, percentage		45.70%	45.70%
CET Electric | Equity Method Investee | Purchase Price of TOTS Project Transfer
Schedule of Equity Method Investments [Line Items]
Purchase price	$ 122
CET Electric | Equity Method Investee | TOTS Project, Lease Payments
Schedule of Equity Method Investments [Line Items]
Payment for easement rights	$ 8
CET Electric | NY Transco
Schedule of Equity Method Investments [Line Items]
Equity method investment		$ 51