Investments Accounted for by the Equity Method and Variable Interest Entities Investments Accounted for by the Equity Method and Variable Interest Entities (Other Equity Inv - Details 3) $ in Millions	Dec. 31, 2016 USD ($) MW	Dec. 31, 2015 USD ($)
Schedule of Equity Method Investments [Line Items]
Equity investments in affiliates	$ 1,120	$ 1,045
Deficit Restoration Obligation	88
Equity Method Investment, Summarized Financial Information, Current Assets	87	84
Equity Method Investments, Summarized Financial Data, Property, Plant and Equipment	1,534	1,807
Equity Method Investments, Summarized Financial Information, Other long-term assets	954	863
Equity Method Investment, Summarized Financial Information, Assets	2,575	2,754
Equity Method Investment, Summarized Financial Information, Current Liabilities	59	56
Equity Method Investments, Summarized Financial Information, Long Term Debt	442	366
Equity Method Investments, Summarized Financial Information, Other long-term liabilities	183	179
Equity Method Investment, Summarized Financial Information, Liabilities	684	601
Equity Method Investment, Summarized Financial Information, Noncontrolling Interest	529	493
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	$ 1,362	$ 1,660
Gladstone Power Station (b)
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	37.50%
Power Generation Capacity, Megawatts | MW	1,613
Equity investments in affiliates	$ 132