Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Per Share data, unless otherwise specified	Jun. 30, 2012	Mar. 31, 2012
Stockholders' Equity
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	100	100
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	800	800
Common stock, shares issued	375	373
Treasury stock, shares	139	138