Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Income Tax Disclosure [Line Items]
Stock Repurchased and Retired During Period, Value	$ 508	$ 1,018	$ 337
Tax Benefits Allocated Directly to Contributed Capital	65	83	22
Gross unrecognized tax benefits	389	331	$ 254	$ 232
Amount of unrecognized tax benefits that would affect the effective tax rate	362
The total amount of unrecognized tax benefits that, if recognized, would result in adjustments to deferred tax assets with corresponding	27
Combined amount of accrued interest and penalties related to uncertain tax positions	14	15
Amount of unrecognized tax benefits for which it is reasonably possible that there will be a reduction within the next 12 months	50
Unremitted earnings of foreign subsidiaries	70	43
Deferred Tax Assets, Valuation Allowance	114	$ 114
Internal Revenue Service (IRS) [Member]
Income Tax Disclosure [Line Items]
Tax credit carry forwards	362
Foreign Country [Member]
Income Tax Disclosure [Line Items]
Undistributed Earnings of Foreign Subsidiaries	1,845
Tax credit carry forwards	7
State [Member]
Income Tax Disclosure [Line Items]
Net operating Loss Carryforwards	871
Net operating loss attributable to various acquired companies	99
Tax credit carry forwards	$ 96