Financial Instruments (Fair Value Of Short-Term Investments By Stated Maturity Date Schedule) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Mar. 31, 2013
Financial Instruments
Short-term investments, Fair Value	$ 328	$ 388	[1]
Short-Term Investments
Financial Instruments
Due in 1 year or less, Amortized Cost	114	160
Due in 1-2 years, Amortized Cost	98	126
Due in 2-3 years, Amortized Cost	109	101
Due in 3-4 years, Amortized Cost	6	0
Short-term investments, Amortized Cost	327	387
Due in 1 year or less, Fair Value	114	160
Due in 1-2 years, Fair Value	99	127
Due in 2-3 years, Fair Value	109	101
Due in 3-4 years, Fair Value	6	0
Short-term investments, Fair Value	$ 328	$ 388

[1] Derived from audited consolidated financial statements.