Financial Instruments (Fair Value Of Short-Term Investments) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013
Financial Instruments
Fair Value	$ 355	$ 388	[1]
Short-Term Investments
Financial Instruments
Cost or Amortized Cost	356	387
Gross Unrealized Gains	0	1
Gross Unrealized Losses	1	0
Fair Value	355	388
Short-Term Investments | Corporate bonds
Financial Instruments
Cost or Amortized Cost	194	177
Gross Unrealized Gains	0	1
Gross Unrealized Losses	1	0
Fair Value	193	178
Short-Term Investments | U.S. agency securities
Financial Instruments
Cost or Amortized Cost	69	76
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	69	76
Short-Term Investments | U.S. Treasury securities
Financial Instruments
Cost or Amortized Cost	53	85
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	53	85
Short-Term Investments | Commercial Paper
Financial Instruments
Cost or Amortized Cost	40	49
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 40	$ 49

[1] Derived from audited consolidated financial statements.