Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Taxes (Textual) [Abstract]
Income tax expense (benefit)	$ 106	$ 105	$ (12)	$ 235
Net discrete tax benefit recognized primarily from completion of federal income tax returns examination			179
Estimated annual effective tax rate, which excludes impact of discrete items			29.70%	33.00%
Expected fiscal year 2014 effective tax rate			14.00%
Reduction in uncertain tax positions resulting from completion of federal income tax returns examination			221
Cash refund received from completion of federal income tax returns examination	$ 70		$ 70