Goodwill And Acquisition-Related Intangibles, Net (Schedule Of Acquisition-Related Intangibles) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Mar. 31, 2020
Finite-Lived Intangible Assets
Gross carrying amount	$ 725	$ 725
Accumulated amortization	(688)	(672)
Acquisition-related intangibles, net	37	53	[1]
Developed And Core Technology
Finite-Lived Intangible Assets
Gross carrying amount	474	474
Accumulated amortization	(458)	(450)
Acquisition-related intangibles, net	16	24
Trade Names And Trademarks
Finite-Lived Intangible Assets
Gross carrying amount	161	161
Accumulated amortization	(140)	(132)
Acquisition-related intangibles, net	21	29
Registered User Base And Other Intangibles
Finite-Lived Intangible Assets
Gross carrying amount	5	5
Accumulated amortization	(5)	(5)
Acquisition-related intangibles, net	0	0
Carrier Contracts And Related
Finite-Lived Intangible Assets
Gross carrying amount	85	85
Accumulated amortization	(85)	(85)
Acquisition-related intangibles, net	$ 0	$ 0

[1] Derived from audited Consolidated Financial Statements.