Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Line Items]
Income Tax Expense (Benefit)	$ 180	$ (1,531)	$ 60
Gross unrecognized tax benefits	584	983	$ 417	$ 457
Amount of unrecognized tax benefits that would affect the effective tax rate	319
Combined amount of accrued interest and penalties related to uncertain tax positions	34	34
Deferred Tax Assets, Valuation Allowance	230	288
Deferred Tax Assets, Gross	2,401	2,328
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability	103	1,760
Deferred Tax Assets, Net	2,002	1,902
Decrease in Unrecognized Tax Benefits is Reasonably Possible	5
Deferred Tax Asset, Intra-entity Transfer, Asset Other than Inventory	$ 1,781	$ 1,818
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	21.00%	21.00%
State [Member]
Income Tax Disclosure [Line Items]
Net operating Loss Carryforwards	$ 2,100
Net operating loss attributable to Switzerland	1,800
Net operating loss attributable to California	146
Tax credit carry forwards	156
Reduction in Taxes [Member]
Income Tax Disclosure [Line Items]
Income Tax Expense (Benefit)	$ 180	$ 80
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability		393
Swiss Federal Tax Administration (FTA) [Member]
Income Tax Disclosure [Line Items]
Deferred Tax Assets, Valuation Allowance		131
Deferred Tax Assets, Net		$ 1,840