Derivative Instruments and Hedging Activities (Details 2) (USD $) In Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Impact of periodic settlements of active swap agreements and the impact of terminated swap agreements on our results of operations
Decrease to interest expense due to hedge accounting for interest rate swaps for periodic settlements of active swap agreements	$ 7	[1]	$ 6	[1]	$ 18	[1]	$ 24	[1]
Decrease to interest expense due to hedge accounting for interest rate swaps for terminated swap agreements	2		4		8		15
Total	$ 9		$ 10		$ 26		$ 39

[1] These amounts represent the net of our periodic variable-rate interest obligations and the swap counterparties? fixed-rate interest obligations. Our variable-rate obligations are based on a spread from the three-month LIBOR.