Fair Value Measurements (Details) (Segment, Continuing Operations [Member], Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Assets:
ARO Trust investments	$ 25	$ 40
Available-for-sale equity securities	24	0
Total derivatives, assets	1	0
Total assets	50	40
Level 1 [Member]
Assets:
ARO Trust investments	25	40
Available-for-sale equity securities	24	0
Total derivatives, assets	1	0
Total assets	50	40
Level 2 [Member]
Assets:
ARO Trust investments	0	0
Available-for-sale equity securities	0	0
Total derivatives, assets	0	0
Total assets	0	0
Level 3 [Member]
Assets:
ARO Trust investments	0	0
Available-for-sale equity securities	0	0
Total derivatives, assets	0	0
Total assets	$ 0	$ 0