Financial Instruments (Fair Value Of Short-Term Investments) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2015	Mar. 31, 2015
Financial Instruments
Fair Value	$ 966	$ 953	[1]
Short-Term Investments
Financial Instruments
Cost or Amortized Cost	968	952
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(2)	0
Fair Value	966	953
Short-Term Investments | Corporate bonds
Financial Instruments
Cost or Amortized Cost	579	467
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	0
Fair Value	578	467
Short-Term Investments | U.S. Treasury securities
Financial Instruments
Cost or Amortized Cost	196	214
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	0
Fair Value	195	214
Short-Term Investments | U.S. agency securities
Financial Instruments
Cost or Amortized Cost	154	161
Gross Unrealized Gains	0	1
Gross Unrealized Losses	0	0
Fair Value	154	162
Short-Term Investments | Commercial paper
Financial Instruments
Cost or Amortized Cost	39	110
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 39	$ 110

[1] Derived from audited Consolidated Financial Statements.