Use of Collateral (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Use of Collateral [Abstract]
Margin deposits	$ 107	[1]	$ 96	[1]
Natural gas and power prepayments	21		22
Total margin deposits and natural gas and power prepayments with our counterparties	128	[2]	118	[2]
Letters of credit issued	459		450
First priority liens under power and natural gas agreements	33		48
First priority liens under interest rate swap agreements	120		116
Total letters of credit and first priority liens with our counterparties	612		614
Margin deposits held by us posted by our counterparties	40	[1],[3]	47	[1],[3]
Letters of credit posted with us by our counterparties	60		61
Total margin deposits and letters of credit posted with us by our counterparties	100		108
Use of Collateral (Textuals) [Abstract]
Margin And Prepayment Amounts Included In Other Assets	13		9
Margin And Prepayment Amounts Included In Margin Deposits And Other Prepaid Expenses	$ 115		$ 109

[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 5 for further discussion of our derivative instruments subject to master netting arrangements.

[2] At March 31, 2015 and December 31, 2014, $115 million and $109 million, respectively, were included in margin deposits and other prepaid expense and $13 million and $9 million, respectively, were included in other assets on our Consolidated Condensed Balance Sheets.

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