(Fair Value Of Short-Term Investments By Stated Maturity Date Schedule) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Mar. 31, 2017
Financial Instruments [Line Items]
Short-term investments, Fair Value	$ 1,073	$ 1,967
Short-Term Investments [Member]
Financial Instruments [Line Items]
Short-term investments, Amortized Cost	1,082	1,970
Short-term investments, Fair Value	1,073	1,967
Due in 1 year or less, Amortized Cost	521	1,237
Due in 1 year or less, Fair Value	520	1,236
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis	561	721
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Fair Value	553	719
Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Amortized Cost Basis	0	12
Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Fair Value	$ 0	$ 12