(Schedule Of Acquisition-Related Intangibles) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Mar. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 725	$ 725
Accumulated amortization	(672)	(638)
Acquisition-related intangibles, net	53	87
Developed And Core Technology
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	474	469
Accumulated amortization	(450)	(427)
Acquisition-related intangibles, net	24	42
Trade Names And Trademarks
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	161	161
Accumulated amortization	(132)	(121)
Acquisition-related intangibles, net	29	40
Registered User Base And Other Intangibles
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	5	5
Accumulated amortization	(5)	(5)
Acquisition-related intangibles, net	0	0
Carrier Contracts And Related
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	85	85
Accumulated amortization	(85)	(85)
Acquisition-related intangibles, net	0	0
In Process Research and Development [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	0	5
Accumulated amortization	0	0
Acquisition-related intangibles, net	$ 0	$ 5