Financial Instruments (Fair Value Of Short-Term Investments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Mar. 31, 2012
Financial Instruments
Fair Value	$ 275	$ 437	[1]
Short-Term Investments
Financial Instruments
Cost or Amortized Cost	274	436
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Fair Value	275	437
Short-Term Investments | Corporate bonds
Financial Instruments
Cost or Amortized Cost	148	149
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Fair Value	149	150
Short-Term Investments | U.S. agency securities
Financial Instruments
Cost or Amortized Cost	68	116
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	68	116
Short-Term Investments | U.S. Treasury securities
Financial Instruments
Cost or Amortized Cost	56	166
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	56	166
Short-Term Investments | Commercial Paper
Financial Instruments
Cost or Amortized Cost	2	5
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 2	$ 5

[1] Derived from audited consolidated financial statements.