Unrealized Losses on Debt Investments (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Jun. 30, 2020
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	$ 11,389	$ 4,552
Less than 12 Months - Unrealized Losses	(132)	(31)
12 Months or Greater - Fair Value	127	0
12 Months or Greater - Unrealized Losses	(3)	0
Total Fair Value	11,516	4,552
Total Unrealized Losses	(135)	(31)
U.S. government and agency securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	5,294	2,323
Less than 12 Months - Unrealized Losses	(111)	(1)
12 Months or Greater - Fair Value	0	0
12 Months or Greater - Unrealized Losses	0	0
Total Fair Value	5,294	2,323
Total Unrealized Losses	(111)	(1)
Foreign government bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	3,148	500
Less than 12 Months - Unrealized Losses	(1)	(3)
12 Months or Greater - Fair Value	5	0
12 Months or Greater - Unrealized Losses	(1)	0
Total Fair Value	3,153	500
Total Unrealized Losses	(2)	(3)
Mortgage- and asset-backed securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	1,211	1,014
Less than 12 Months - Unrealized Losses	(5)	(6)
12 Months or Greater - Fair Value	87	0
12 Months or Greater - Unrealized Losses	(1)	0
Total Fair Value	1,298	1,014
Total Unrealized Losses	(6)	(6)
Corporate notes and bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	1,678	649
Less than 12 Months - Unrealized Losses	(8)	(17)
12 Months or Greater - Fair Value	34	0
12 Months or Greater - Unrealized Losses	(1)	0
Total Fair Value	1,712	649
Total Unrealized Losses	(9)	(17)
Municipal securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	58	66
Less than 12 Months - Unrealized Losses	(7)	(4)
12 Months or Greater - Fair Value	1	0
12 Months or Greater - Unrealized Losses	0	0
Total Fair Value	59	66
Total Unrealized Losses	$ (7)	$ (4)