Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 73	$ 101	$ 160	$ (21)
Net discrete tax benefit recognized primarily from resolutions of uncertain tax positions upon completion of U.S. federal income tax returns examination	$ 19		$ 19	$ 179
Estimated annual effective tax rate, which excludes impact of discrete items			29.20%	29.20%
Expected fiscal year 2015 effective tax rate			30.00%