v3.7.0.1
Unrealized Losses on Investments (Detail) - USD ($)
$ in Millions
Jun. 30, 2017
Jun. 30, 2016
Unrealized Losses on Investments [Line Items]    
Less than 12 Months - Fair Value $ 93,370 $ 12,188
Less than 12 Months - Unrealized Losses (367) (165)
12 Months or Greater - Fair Value 917 1,967
12 Months or Greater - Unrealized Losses (56) (137)
Total Fair Value 94,287 14,155
Total Unrealized Losses (423) (302)
U.S. government and agency securities    
Unrealized Losses on Investments [Line Items]    
Less than 12 Months - Fair Value 87,558 5,816
Less than 12 Months - Unrealized Losses (348) (3)
12 Months or Greater - Fair Value 371 432
12 Months or Greater - Unrealized Losses (12) (8)
Total Fair Value 87,929 6,248
Total Unrealized Losses (360) (11)
Foreign government bonds    
Unrealized Losses on Investments [Line Items]    
Less than 12 Months - Fair Value 4,006 3,452
Less than 12 Months - Unrealized Losses (2) (3)
12 Months or Greater - Fair Value 23 35
12 Months or Greater - Unrealized Losses (11) (15)
Total Fair Value 4,029 3,487
Total Unrealized Losses (13) (18)
Mortgage- and asset-backed securities    
Unrealized Losses on Investments [Line Items]    
Less than 12 Months - Fair Value 1,068 844
Less than 12 Months - Unrealized Losses (3) (1)
12 Months or Greater - Fair Value 198 322
12 Months or Greater - Unrealized Losses (1) (1)
Total Fair Value 1,266 1,166
Total Unrealized Losses (4) (2)
Corporate notes and bonds    
Unrealized Losses on Investments [Line Items]    
Less than 12 Months - Fair Value 669 1,180
Less than 12 Months - Unrealized Losses (8) (11)
12 Months or Greater - Fair Value 177 788
12 Months or Greater - Unrealized Losses (4) (24)
Total Fair Value 846 1,968
Total Unrealized Losses (12) (35)
Common and preferred stock    
Unrealized Losses on Investments [Line Items]    
Less than 12 Months - Fair Value 69 896
Less than 12 Months - Unrealized Losses (6) (147)
12 Months or Greater - Fair Value 148 390
12 Months or Greater - Unrealized Losses (28) (89)
Total Fair Value 217 1,286
Total Unrealized Losses $ (34) $ (236)