Financial Instruments (Fair Value Of Short-Term Investments) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020
Financial Instruments
Fair Value	$ 1,947	$ 1,967	[1]
Short-term investments
Financial Instruments
Cost or Amortized Cost	1,939	1,970
Gross Unrealized Gains	8	5
Gross Unrealized Losses	0	(8)
Fair Value	1,947	1,967
Short-term investments | Corporate bonds
Financial Instruments
Cost or Amortized Cost	534	684
Gross Unrealized Gains	3	1
Gross Unrealized Losses	0	(4)
Fair Value	537	681
Short-term investments | U.S. Treasury securities
Financial Instruments
Cost or Amortized Cost	717	530
Gross Unrealized Gains	3	4
Gross Unrealized Losses	0	0
Fair Value	720	534
Short-term investments | U.S. agency securities
Financial Instruments
Cost or Amortized Cost	8	8
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	8	8
Short-term investments | Commercial paper
Financial Instruments
Cost or Amortized Cost	334	377
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	334	377
Short-term investments | Debt Security, Government, Non-US [Member]
Financial Instruments
Cost or Amortized Cost	33	42
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	33	42
Short-term investments | Asset-backed Securities [Member]
Financial Instruments
Cost or Amortized Cost	250	273
Gross Unrealized Gains	2	0
Gross Unrealized Losses	0	(4)
Fair Value	252	269
Short-term investments | Certificates of Deposit [Member]
Financial Instruments
Cost or Amortized Cost	63	56
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 63	$ 56

[1] Derived from audited Consolidated Financial Statements.