Unrealized Losses on Debt Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Jun. 30, 2020
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	$ 5,914	$ 4,552
Less than 12 Months - Unrealized Losses	(26)	(31)
12 Months or Greater - Fair Value	0	0
12 Months or Greater - Unrealized Losses	0	0
Total Fair Value	5,914	4,552
Total Unrealized Losses	(26)	(31)
U.S. government and agency securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	2,777	2,323
Less than 12 Months - Unrealized Losses	(12)	(1)
12 Months or Greater - Fair Value	0	0
12 Months or Greater - Unrealized Losses	0	0
Total Fair Value	2,777	2,323
Total Unrealized Losses	(12)	(1)
Foreign government bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	1,708	500
Less than 12 Months - Unrealized Losses	(1)	(3)
12 Months or Greater - Fair Value	0	0
12 Months or Greater - Unrealized Losses	0	0
Total Fair Value	1,708	500
Total Unrealized Losses	(1)	(3)
Mortgage- and asset-backed securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	1,148	1,014
Less than 12 Months - Unrealized Losses	(4)	(6)
12 Months or Greater - Fair Value	0	0
12 Months or Greater - Unrealized Losses	0	0
Total Fair Value	1,148	1,014
Total Unrealized Losses	(4)	(6)
Corporate notes and bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	160	649
Less than 12 Months - Unrealized Losses	(1)	(17)
12 Months or Greater - Fair Value	0	0
12 Months or Greater - Unrealized Losses	0	0
Total Fair Value	160	649
Total Unrealized Losses	(1)	(17)
Municipal securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	121	66
Less than 12 Months - Unrealized Losses	(8)	(4)
12 Months or Greater - Fair Value	0	0
12 Months or Greater - Unrealized Losses	0	0
Total Fair Value	121	66
Total Unrealized Losses	$ (8)	$ (4)