Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2012	Mar. 31, 2011
Stockholders' Equity
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	800,000,000	800,000,000
Common stock, shares issued	373,000,000	369,000,000
Treasury stock, shares	138,000,000	117,000,000