Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 87	$ (122)
Net discrete tax benefit recognized primarily from completion of federal income tax returns examination		181
Estimated annual effective tax rate, which excludes impact of discrete items	29.00%	28.50%
Expected fiscal year 2015 effective tax rate	30.00%
Timing of resolution of income tax examinations	12 months
Period of unrecognized tax benefit	12 months
Significant change in unrecognized tax benefits is reasonably possible within next 12 months, Estimated range of change, Upper bound	$ 30