Unrealized Losses on Debt Investments (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Jun. 30, 2019
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	$ 6,876	$ 2,678
Less than 12 Months - Unrealized Losses	(27)	(5)
12 Months or Greater - Fair Value	26,281	39,989
12 Months or Greater - Unrealized Losses	(52)	(117)
Total Fair Value	33,157	42,667
Total Unrealized Losses	(79)	(122)
U.S. government and agency securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	4,169	1,491
Less than 12 Months - Unrealized Losses	(18)	(1)
12 Months or Greater - Fair Value	25,788	39,158
12 Months or Greater - Unrealized Losses	(39)	(103)
Total Fair Value	29,957	40,649
Total Unrealized Losses	(57)	(104)
Foreign government bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	1,464	25
Less than 12 Months - Unrealized Losses	(3)	0
12 Months or Greater - Fair Value	63	77
12 Months or Greater - Unrealized Losses	(8)	(8)
Total Fair Value	1,527	102
Total Unrealized Losses	(11)	(8)
Mortgage- and asset-backed securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	563	664
Less than 12 Months - Unrealized Losses	(1)	(1)
12 Months or Greater - Fair Value	198	378
12 Months or Greater - Unrealized Losses	(1)	(2)
Total Fair Value	761	1,042
Total Unrealized Losses	(2)	(3)
Corporate notes and bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	680	498
Less than 12 Months - Unrealized Losses	(5)	(3)
12 Months or Greater - Fair Value	231	376
12 Months or Greater - Unrealized Losses	(4)	(4)
Total Fair Value	911	874
Total Unrealized Losses	(9)	$ (7)
Municipal securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	0
Less than 12 Months - Unrealized Losses	0
12 Months or Greater - Fair Value	1
12 Months or Greater - Unrealized Losses	0
Total Fair Value	1
Total Unrealized Losses	$ 0