Debt (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Debt Disclosure [Abstract]
Total interest expense on short-term and long-term debt, net of amounts capitalized	$ 2	$ 3	$ 4	$ 7
Fair value of long-term debt	$ 314		$ 314		$ 311