Unrealized Losses on Debt Investments (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Jun. 30, 2019
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	$ 7,908	$ 2,678
Less than 12 Months - Unrealized Losses	(173)	(5)
12 Months or Greater - Fair Value	556	39,989
12 Months or Greater - Unrealized Losses	(33)	(117)
Total Fair Value	8,464	42,667
Total Unrealized Losses	(206)	(122)
U.S. government and agency securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	1,703	1,491
Less than 12 Months - Unrealized Losses	(4)	(1)
12 Months or Greater - Fair Value	372	39,158
12 Months or Greater - Unrealized Losses	(9)	(103)
Total Fair Value	2,075	40,649
Total Unrealized Losses	(13)	(104)
Foreign government bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	481	25
Less than 12 Months - Unrealized Losses	(6)	0
12 Months or Greater - Fair Value	8	77
12 Months or Greater - Unrealized Losses	(7)	(8)
Total Fair Value	489	102
Total Unrealized Losses	(13)	(8)
Mortgage- and asset-backed securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	2,180	664
Less than 12 Months - Unrealized Losses	(32)	(1)
12 Months or Greater - Fair Value	134	378
12 Months or Greater - Unrealized Losses	(5)	(2)
Total Fair Value	2,314	1,042
Total Unrealized Losses	(37)	(3)
Corporate notes and bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	3,469	498
Less than 12 Months - Unrealized Losses	(126)	(3)
12 Months or Greater - Fair Value	41	376
12 Months or Greater - Unrealized Losses	(12)	(4)
Total Fair Value	3,510	874
Total Unrealized Losses	(138)	$ (7)
Municipal securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	75
Less than 12 Months - Unrealized Losses	(5)
12 Months or Greater - Fair Value	1
12 Months or Greater - Unrealized Losses	0
Total Fair Value	76
Total Unrealized Losses	$ (5)