Unrealized Losses on Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Jun. 30, 2015
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	$ 85,474	$ 18,789
Less than 12 Months - Unrealized Losses	(513)	(236)
12 Months or Greater - Fair Value	1,764	719
12 Months or Greater - Unrealized Losses	(206)	(77)
Total Fair Value	87,238	19,508
Total Unrealized Losses	(719)	(313)
U.S. government and agency securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	72,914	6,636
Less than 12 Months - Unrealized Losses	(202)	(9)
12 Months or Greater - Fair Value	566	421
12 Months or Greater - Unrealized Losses	(30)	(21)
Total Fair Value	73,480	7,057
Total Unrealized Losses	(232)	(30)
Foreign government bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	3,635	4,611
Less than 12 Months - Unrealized Losses	(9)	(12)
12 Months or Greater - Fair Value	52	18
12 Months or Greater - Unrealized Losses	(30)	(12)
Total Fair Value	3,687	4,629
Total Unrealized Losses	(39)	(24)
Mortgage- and asset-backed securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	3,428	3,171
Less than 12 Months - Unrealized Losses	(9)	(5)
12 Months or Greater - Fair Value	329	28
12 Months or Greater - Unrealized Losses	0	(1)
Total Fair Value	3,757	3,199
Total Unrealized Losses	(9)	(6)
Corporate notes and bonds
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	4,168	2,946
Less than 12 Months - Unrealized Losses	(68)	(29)
12 Months or Greater - Fair Value	377	104
12 Months or Greater - Unrealized Losses	(38)	(8)
Total Fair Value	4,545	3,050
Total Unrealized Losses	(106)	(37)
Municipal securities
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value		36
Less than 12 Months - Unrealized Losses		(1)
12 Months or Greater - Fair Value		0
12 Months or Greater - Unrealized Losses		0
Total Fair Value		36
Total Unrealized Losses		(1)
Common and preferred stock
Unrealized Losses on Investments [Line Items]
Less than 12 Months - Fair Value	1,329	1,389
Less than 12 Months - Unrealized Losses	(225)	(180)
12 Months or Greater - Fair Value	440	148
12 Months or Greater - Unrealized Losses	(108)	(35)
Total Fair Value	1,769	1,537
Total Unrealized Losses	$ (333)	$ (215)