Financial Instruments (Fair Value Of Short-Term Investments By Stated Maturity Date Schedule) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Mar. 31, 2014
Financial Instruments
Short-term investments, Fair Value	$ 764	$ 583	[1]
Short-Term Investments
Financial Instruments
Due in 1 year or less, Amortized Cost	345	318
Due in 1-2 years, Amortized Cost	203	156
Due in 2-3 years, Amortized Cost	209	104
Due in 3-4 years, Amortized Cost	7	5
Short-term investments, Amortized Cost	764	583
Due in 1 year or less, Fair Value	345	318
Due in 1-2 years, Fair Value	203	156
Due in 2-3 years, Fair Value	209	104
Due in 3-4 years, Fair Value	7	5
Short-term investments, Fair Value	$ 764	$ 583

[1] Derived from audited consolidated financial statements.