Unrealized Losses on Debt Investments (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Jun. 30, 2023
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	$ 3,018	$ 10,721
Less than 12 Months - Unrealized Losses	(89)	(398)
12 Months or Greater - Fair Value	59,872	53,598
12 Months or Greater - Unrealized Losses	(4,783)	(4,152)
Total Fair Value	62,890	64,319
Total Unrealized Losses	(4,872)	(4,550)
U.S. government and agency securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	526	7,950
Less than 12 Months - Unrealized Losses	(23)	(336)
12 Months or Greater - Fair Value	51,241	45,273
12 Months or Greater - Unrealized Losses	(4,124)	(3,534)
Total Fair Value	51,767	53,223
Total Unrealized Losses	(4,147)	(3,870)
Foreign government bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	72	77
Less than 12 Months - Unrealized Losses	(4)	(5)
12 Months or Greater - Fair Value	411	391
12 Months or Greater - Unrealized Losses	(20)	(19)
Total Fair Value	483	468
Total Unrealized Losses	(24)	(24)
Mortgage- and asset-backed securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	309	257
Less than 12 Months - Unrealized Losses	(12)	(5)
12 Months or Greater - Fair Value	417	412
12 Months or Greater - Unrealized Losses	(40)	(34)
Total Fair Value	726	669
Total Unrealized Losses	(52)	(39)
Corporate notes and bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	2,044	2,326
Less than 12 Months - Unrealized Losses	(49)	(49)
12 Months or Greater - Fair Value	7,568	7,336
12 Months or Greater - Unrealized Losses	(563)	(534)
Total Fair Value	9,612	9,662
Total Unrealized Losses	(612)	(583)
Municipal securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	67	111
Less than 12 Months - Unrealized Losses	(1)	(3)
12 Months or Greater - Fair Value	235	186
12 Months or Greater - Unrealized Losses	(36)	(31)
Total Fair Value	302	297
Total Unrealized Losses	$ (37)	$ (34)