Quarterly Financial And Market Information (Summary Of Quarterly Financial And Market Information) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Quarterly Financial And Market Information [Line Items]
Net revenue	$ 1,387	$ 1,593	$ 1,348	$ 1,209	$ 1,238	$ 1,289	$ 1,286	$ 1,137	$ 5,537	$ 4,950	$ 5,150
Gross profit	1,118	1,085	943	1,022	962	876	868	922	4,168	3,628	3,873
Operating income (loss)	401	361	268	415	196	242	258	300	1,445	996	1,434
Net income (loss)	$ 418	$ 346	$ 854	$ 1,421	$ 209	$ 262	$ 255	$ 293	$ 3,039	$ 1,019	$ 1,043
Earnings Per Share, Basic	$ 1.44	$ 1.18	$ 2.89	$ 4.78	$ 0.70	$ 0.87	$ 0.84	$ 0.96	$ 10.37	$ 3.36	$ 3.39
Earnings Per Share, Diluted	$ 1.43	$ 1.18	$ 2.89	$ 4.75	$ 0.69	$ 0.86	$ 0.83	$ 0.95	$ 10.30	$ 3.33	$ 3.34
Deferred Tax Assets, Net	$ 1,902				$ 33				$ 1,902	$ 33
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability			$ 630	$ 1,170					1,760
Swiss Federal Tax Administration (FTA) [Member]
Quarterly Financial And Market Information [Line Items]
Deferred Tax Assets, Net	$ 1,840								$ 1,840