Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2016	Mar. 31, 2015
Statement of Financial Position [Abstract]
Accumulated depreciation	$ 832	$ 812
Preferred stock, no par value (in dollars per share)	$ 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 (in dollars per share)	$ 0.10	$ 0.10
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	412,596,452	435,502,730
Treasury stock, shares	177,098,629	154,192,351