Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Provision (benefit) for income taxes	$ 69	$ (2,821)	$ 178	$ (2,655)
Effective tax rate	24.00%		26.00%
Income tax benefit attributable to revaluation of net deferred tax liabilities due to reduction of federal statutory income tax rate			$ (2,900)
U.S. federal statutory tax rate	21.00%	35.00%	21.00%	35.00%
Tax Cuts and Jobs Act, Accounting Complete	true		true
Provisional deemed repatriation tax			$ 9
Deferred tax assets	$ 3,000		3,000		$ 1,600
Net deferred income tax liability	$ 5,500		$ 5,500		$ 5,300