(Fair Value Of Short-Term Investments By Stated Maturity Date Schedule) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Mar. 31, 2015
Financial Instruments [Line Items]
Short-term investments, Fair Value	$ 1,341	$ 953
Short-Term Investments [Member]
Financial Instruments [Line Items]
Short-term investments, Amortized Cost	1,339	952
Short-term investments, Fair Value	1,341	953
Due in 1 year or less [Member] | Short-Term Investments [Member]
Financial Instruments [Line Items]
Due in 1 year or less, Amortized Cost	571	417
Due in 1 year or less, Fair Value	571	417
Due in 1-2 years [Member]
Financial Instruments [Line Items]
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis	461	281
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Fair Value	462	281
Due in 2-3 years [Member] | Short-Term Investments [Member]
Financial Instruments [Line Items]
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis	295	244
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Fair Value	296	245
Due in 3-4 years [Member] | Short-Term Investments [Member]
Financial Instruments [Line Items]
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis	12	10
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Fair Value	$ 12	$ 10