Financial Instruments (Fair Value Of Short-Term Investments) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Mar. 31, 2012
Financial Instruments
Fair Value	$ 351	$ 437	[1]
Short-Term Investments
Financial Instruments
Cost or Amortized Cost	350	436
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Fair Value	351	437
Short-Term Investments | Corporate bonds
Financial Instruments
Cost or Amortized Cost	179	149
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Fair Value	180	150
Short-Term Investments | U.S. Treasury securities
Financial Instruments
Cost or Amortized Cost	95	166
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	95	166
Short-Term Investments | U.S. agency securities
Financial Instruments
Cost or Amortized Cost	73	116
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	73	116
Short-Term Investments | Commercial Paper
Financial Instruments
Cost or Amortized Cost	3	5
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 3	$ 5

[1] Derived from audited consolidated financial statements.