Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income tax expense	$ 375	$ 84	$ 509	$ 257
Tax Cuts and Jobs Act [Line Items]
Net discrete tax expense	310		$ 302
Estimated annual effective tax rate excluding impact of discrete items			26.60%	28.90%
Tax Cuts and Jobs Act (Tax Act)
Tax Cuts and Jobs Act [Line Items]
Net discrete tax expense	318
Tax Cuts and Jobs Act (Tax Act) | Taxation of Unremitted Foreign Earnings
Tax Cuts and Jobs Act [Line Items]
Net discrete tax expense	220
Tax Cuts and Jobs Act (Tax Act) | Remeasurement of Deferred Tax Assets and Liabilities
Tax Cuts and Jobs Act [Line Items]
Net discrete tax expense	$ 98
Tax Cuts and Jobs Act (Tax Act) | Statutory Tax Rate Reduction
Tax Cuts and Jobs Act [Line Items]
Estimated annual effective tax rate excluding impact of discrete items	(2.00%)