Unrealized Losses on Debt Investments (Detail) - USD ($) $ in Millions	Sep. 30, 2025	Jun. 30, 2025
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	$ 642	$ 4,560
Less than 12 Months - Unrealized Losses	(55)	(65)
12 Months or Greater - Fair Value	35,879	38,176
12 Months or Greater - Unrealized Losses	(1,301)	(1,560)
Total Fair Value	36,521	42,736
Total Unrealized Losses	(1,356)	(1,625)
U.S. government and agency securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	312	2,569
Less than 12 Months - Unrealized Losses	(52)	(51)
12 Months or Greater - Fair Value	32,625	34,608
12 Months or Greater - Unrealized Losses	(1,186)	(1,411)
Total Fair Value	32,937	37,177
Total Unrealized Losses	(1,238)	(1,462)
Foreign government bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	45	43
Less than 12 Months - Unrealized Losses	(2)	(2)
12 Months or Greater - Fair Value	105	106
12 Months or Greater - Unrealized Losses	(4)	(7)
Total Fair Value	150	149
Total Unrealized Losses	(6)	(9)
Mortgage- and asset-backed securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	0	841
Less than 12 Months - Unrealized Losses	0	(4)
12 Months or Greater - Fair Value	264	189
12 Months or Greater - Unrealized Losses	(23)	(23)
Total Fair Value	264	1,030
Total Unrealized Losses	(23)	(27)
Corporate notes and bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	285	1,107
Less than 12 Months - Unrealized Losses	(1)	(8)
12 Months or Greater - Fair Value	2,718	3,105
12 Months or Greater - Unrealized Losses	(69)	(98)
Total Fair Value	3,003	4,212
Total Unrealized Losses	(70)	(106)
Municipal securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	0	0
Less than 12 Months - Unrealized Losses	0	0
12 Months or Greater - Fair Value	167	168
12 Months or Greater - Unrealized Losses	(19)	(21)
Total Fair Value	167	168
Total Unrealized Losses	$ (19)	$ (21)