Quarterly Financial And Market Information (Summary Of Quarterly Financial And Market Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Quarterly Financial And Market Information [Line Items]
Deferred Tax Assets, Net	$ 2,002	$ 1,902
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability	$ 103	1,760
Swiss Federal Tax Administration (FTA) [Member]
Quarterly Financial And Market Information [Line Items]
Deferred Tax Assets, Net		$ 1,840