Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
Statement of Financial Position [Abstract]
Accumulated depreciation	$ 786	$ 707
Preferred stock, no par value	$ 0	$ 0
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.1	$ 0.1
Common stock, shares authorized	1,100,000,000	1,100,000,000
Common stock, shares issued	589,695,081	589,695,081
Common stock, shares outstanding	448,149,131	466,183,134
Treasury stock, shares	141,545,950	123,511,947