Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Mar. 31, 2016
Income Tax Disclosure [Line Items]
Effective tax rate	37.00%	38.00%	37.00%	37.00%
Provision for income taxes	$ 95	$ 161	$ 241	$ 231
Deferred tax assets	1,300		1,300		$ 1,900
Net deferred income tax liability	$ 8,219		$ 8,219		$ 8,016
Federal [Member]
Income Tax Disclosure [Line Items]
Expiration Dates			Mar. 31, 2035