Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2015
Operating Loss Carryforwards [Line Items]
Effective tax rate	38.00%	38.00%	37.00%	37.00%
Provision for income taxes	$ 210	$ 185	$ 441	$ 574
Deferred tax assets	1,900		1,900		$ 2,200
Net deferred income tax liability	7,848		$ 7,848		$ 7,519
Current federal and state income tax liability	$ 87
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, 2035