Unrealized Losses on Debt Investments (Detail) - USD ($) $ in Millions	Mar. 31, 2025	Jun. 30, 2024
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	$ 2,927	$ 2,157
Less than 12 Months - Unrealized Losses	(70)	(25)
12 Months or Greater - Fair Value	42,949	52,432
12 Months or Greater - Unrealized Losses	(1,893)	(3,323)
Total Fair Value	45,876	54,589
Total Unrealized Losses	(1,963)	(3,348)
U.S. government and agency securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	492	529
Less than 12 Months - Unrealized Losses	(50)	(12)
12 Months or Greater - Fair Value	38,754	45,821
12 Months or Greater - Unrealized Losses	(1,697)	(2,936)
Total Fair Value	39,246	46,350
Total Unrealized Losses	(1,747)	(2,948)
Foreign government bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	66	79
Less than 12 Months - Unrealized Losses	(3)	(2)
12 Months or Greater - Fair Value	127	180
12 Months or Greater - Unrealized Losses	(10)	(14)
Total Fair Value	193	259
Total Unrealized Losses	(13)	(16)
Mortgage- and asset-backed securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	649	201
Less than 12 Months - Unrealized Losses	(3)	(1)
12 Months or Greater - Fair Value	227	409
12 Months or Greater - Unrealized Losses	(24)	(34)
Total Fair Value	876	610
Total Unrealized Losses	(27)	(35)
Corporate notes and bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	1,720	1,310
Less than 12 Months - Unrealized Losses	(14)	(9)
12 Months or Greater - Fair Value	3,629	5,779
12 Months or Greater - Unrealized Losses	(137)	(310)
Total Fair Value	5,349	7,089
Total Unrealized Losses	(151)	(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	212	243
12 Months or Greater - Unrealized Losses	(25)	(29)
Total Fair Value	212	281
Total Unrealized Losses	$ (25)	$ (30)