Stockholders' Equity (Schedule of Treasury Stock) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		53 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012
Stockholders' Equity Note [Abstract]
Shares repurchased	636,710	273,753	12,719,518
Average purchase price per share	$ 45.09	$ 47.54	$ 38.13
Amount spent on repurchased shares	$ 28	$ 13	$ 485