Stockholders' Equity (Schedule of Treasury Stock) (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended			9 Months Ended		56 Months Ended
	Apr. 30, 2011	Oct. 31, 2008	Feb. 29, 2008	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012
Stockholders' Equity Note [Abstract]
Share repurchase plan, authorized repurchase amount	$ 129	$ 100	$ 400			$ 629
Shares repurchased				853,388	591,356	12,936,196
Average purchase price per share				$ 43.19	$ 47.37	$ 38.12
Amount spent on repurchased shares				$ 37	$ 28	$ 493