Unrealized Losses on Debt Investments (Detail) - USD ($) $ in Millions	Sep. 30, 2024	Jun. 30, 2024
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	$ 292	$ 2,157
Less than 12 Months - Unrealized Losses	(4)	(25)
12 Months or Greater - Fair Value	51,876	52,432
12 Months or Greater - Unrealized Losses	(2,045)	(3,323)
Total Fair Value	52,168	54,589
Total Unrealized Losses	(2,049)	(3,348)
U.S. government and agency securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	146	529
Less than 12 Months - Unrealized Losses	(2)	(12)
12 Months or Greater - Fair Value	46,240	45,821
12 Months or Greater - Unrealized Losses	(1,826)	(2,936)
Total Fair Value	46,386	46,350
Total Unrealized Losses	(1,828)	(2,948)
Foreign government bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	12	79
Less than 12 Months - Unrealized Losses	(1)	(2)
12 Months or Greater - Fair Value	144	180
12 Months or Greater - Unrealized Losses	(8)	(14)
Total Fair Value	156	259
Total Unrealized Losses	(9)	(16)
Mortgage- and asset-backed securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	0	201
Less than 12 Months - Unrealized Losses	0	(1)
12 Months or Greater - Fair Value	287	409
12 Months or Greater - Unrealized Losses	(22)	(34)
Total Fair Value	287	610
Total Unrealized Losses	(22)	(35)
Corporate notes and bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	134	1,310
Less than 12 Months - Unrealized Losses	(1)	(9)
12 Months or Greater - Fair Value	4,963	5,779
12 Months or Greater - Unrealized Losses	(166)	(310)
Total Fair Value	5,097	7,089
Total Unrealized Losses	(167)	(319)
Municipal securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	0	38
Less than 12 Months - Unrealized Losses	0	(1)
12 Months or Greater - Fair Value	242	243
12 Months or Greater - Unrealized Losses	(23)	(29)
Total Fair Value	242	281
Total Unrealized Losses	$ (23)	$ (30)