Use of Collateral (Details) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Financial Instruments Owned and Pledged as Collateral [Line Items]
Margin deposits	[1]	$ 120	$ 89
Natural gas and power prepayments		27	34
Total margin deposits and natural gas and power prepayments with our counterparties	[2]	147	123
Letters of credit issued		586	600
First priority liens under power and natural gas agreements	[3]	299	382
First priority liens under interest rate hedging instruments		83	92
Total letters of credit and first priority liens with our counterparties		968	1,074
Margin deposits held by us posted by our counterparties	[1],[4]	30	35
Letters of credit posted with us by our counterparties		35	24
Total margin deposits and letters of credit posted with us by our counterparties		65	59
Use of Collateral (Textuals) [Abstract]
Margin And Prepayment Amounts Included In Other Assets		9	22
Margin And Prepayment Amounts Included In Margin Deposits And Other Prepaid Expenses		138	101
Champion Energy [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
First priority liens under power and natural gas agreements		$ 268	$ 345

[1] Balances are subject to master netting arrangements and presented on a gross basis on our Consolidated Condensed Balance Sheets. We do not offset fair value amounts recognized for derivative instruments executed with the same counterparty under a master netting arrangement for financial statement presentation, and we do not offset amounts recognized for the right to reclaim, or the obligation to return, cash collateral with corresponding derivative instrument fair values. See Note 6 for further discussion of our derivative instruments subject to master netting arrangements.

[2] At September 30, 2016 and December 31, 2015, $138 million and $101 million, respectively, were included in margin deposits and other prepaid expense and $9 million and $22 million, respectively, were included in other assets on our Consolidated Condensed Balance Sheets.

[3] Includes $268 million and $345 million related to first priority liens under power supply contracts associated with our retail hedging activities at September 30, 2016 and December 31, 2015, respectively.

[4] Included in other current liabilities on our Consolidated Condensed Balance Sheets.