Shareholders' Equity (Schedule of Treasury Stock) (Details) (USD $) In Millions, except Share data	9 Months Ended		44 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011
Stockholders' Equity Note [Abstract]
Shares repurchased	591,356	1,473,492	12,022,148
Average purchase price per share	$ 47.37	$ 27.82	$ 37.74
Amount spent on repurchased shares	$ 28	$ 41	$ 454