Use of Collateral (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Use of Collateral [Abstract]
Margin deposits	$ 276	[1]	$ 196	[1]
Natural gas and power prepayments	33		35
Total margin deposits and natural gas and power prepayments with our counterparties	309	[2]	231	[2]
Letters of credit issued	486		484
First priority liens under power and natural gas agreements	21		14
First priority liens under interest rate swap agreements	150		206
Total letters of credit and first priority liens with our counterparties	657		704
Margin deposits held by us posted by our counterparties	3	[1],[3]	11	[1],[3]
Letters of credit posted with us by our counterparties	1		1
Total margin deposits and letters of credit posted with us by our counterparties	4		12
Use of Collateral (Textuals) [Abstract]
Margin And Prepayment Amounts Included In Other Assets	18		20
Margin And Prepayment Amounts Included In Margin Deposits And Other Prepaid Expenses	$ 291		$ 211

[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 June 30, 2013 and December 31, 2012, $291 million and $211 million, respectively, were included in margin deposits and other prepaid expense and $18 million and $20 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.