Income Taxes (Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Line Items]
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent	$ 101
Accruals, reserves and other expenses		$ 81
Tax credit carryforwards	140	121
Stock-based compensation	33	24
Net operating loss & capital loss carryforwards	22	23
Total	296	249
Valuation allowance	(162)	(138)
Deferred tax assets, net of valuation allowance	134	111
Amortization and Depreciation	(28)	(27)
Deferred Tax Liabilities, Gross, Noncurrent	(66)	0
Prepaids and other liabilities	(7)	(2)
Total	(101)	(29)
Deferred tax assets, net of valuation allowance and deferred tax liabilities	$ 33	$ 82