Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Per Share data	Sep. 30, 2011	Mar. 31, 2011
Stockholders' equity:
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, authorized	1.0	1.0
Preferred stock, issued
Preferred stock, outstanding
Common stock, par value	$ 0.01	$ 0.01
Common stock, authorized	600.0	600.0
Common stock, issued	249.1	249.1
Treasury stock, shares at cost	78.5	71.9