Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2015
Operating Loss Carryforwards [Line Items]
Effective tax rate	38.00%	38.00%	37.00%	37.00%
Provision for income taxes	$ 161	$ 176	$ 231	$ 389
Deferred tax assets	2,100		2,100		$ 2,200
Net deferred income tax liability	$ 7,700		$ 7,700		$ 7,500
Expiration Beginning Date [Member]
Operating Loss Carryforwards [Line Items]
Expiration Dates			Mar. 31, 2029
Expiration Ending Date [Member]
Operating Loss Carryforwards [Line Items]
Expiration Dates			Mar. 31, 2036