Financial Instruments (Fair Value Of Short-Term Investments) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019
Financial Instruments
Fair Value	$ 1,654	$ 737	[1]
Short-term investments
Financial Instruments
Cost or Amortized Cost	1,652	738
Gross Unrealized Gains	2	0
Gross Unrealized Losses	0	(1)
Fair Value	1,654	737
Short-term investments | Corporate bonds
Financial Instruments
Cost or Amortized Cost	635	325
Gross Unrealized Gains	2	0
Gross Unrealized Losses	0	(1)
Fair Value	637	324
Short-term investments | U.S. Treasury securities
Financial Instruments
Cost or Amortized Cost	489	153
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	489	153
Short-term investments | U.S. agency securities
Financial Instruments
Cost or Amortized Cost	31	44
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	31	44
Short-term investments | Commercial paper
Financial Instruments
Cost or Amortized Cost	189	112
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	189	112
Short-term investments | Debt Security, Government, Non-US [Member]
Financial Instruments
Cost or Amortized Cost	48	50
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	48	50
Short-term investments | Asset-backed Securities [Member]
Financial Instruments
Cost or Amortized Cost	242	53
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	242	53
Short-term investments | Certificates of Deposit [Member]
Financial Instruments
Cost or Amortized Cost	18	1
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 18	$ 1

[1] Derived from audited Consolidated Financial Statements.