Unaudited Quarterly Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues	$ 1,551	$ 954	$ 846	$ 1,550	$ 1,608	$ 1,171	$ 1,228	$ 2,095	$ 4,901	$ 6,102	$ 6,569
Operating Income (Loss)	211	(152)	106	229	177	111	114	260	394	662	667
Net Income (Loss)	$ 104	$ (127)	$ 42	$ 118	$ 93	$ 43	$ 47	$ 133	$ 137	$ 316	$ 300