v3.8.0.1
Unrealized Losses on Investments (Detail) - USD ($)
$ in Millions
Mar. 31, 2018
Jun. 30, 2017
Unrealized Losses on Investments [Line Items]    
Less than 12 Months - Fair Value $ 101,301 $ 93,370
Less than 12 Months - Unrealized Losses (1,210) (367)
12 Months or Greater - Fair Value 2,657 917
12 Months or Greater - Unrealized Losses (101) (56)
Total Fair Value 103,958 94,287
Total Unrealized Losses (1,311) (423)
U.S. government and agency securities    
Unrealized Losses on Investments [Line Items]    
Less than 12 Months - Fair Value 95,908 87,558
Less than 12 Months - Unrealized Losses (1,169) (348)
12 Months or Greater - Fair Value 2,031 371
12 Months or Greater - Unrealized Losses (70) (12)
Total Fair Value 97,939 87,929
Total Unrealized Losses (1,239) (360)
Foreign government bonds    
Unrealized Losses on Investments [Line Items]    
Less than 12 Months - Fair Value 1,261 4,006
Less than 12 Months - Unrealized Losses (3) (2)
12 Months or Greater - Fair Value 26 23
12 Months or Greater - Unrealized Losses (9) (11)
Total Fair Value 1,287 4,029
Total Unrealized Losses (12) (13)
Mortgage- and asset-backed securities    
Unrealized Losses on Investments [Line Items]    
Less than 12 Months - Fair Value 1,614 1,068
Less than 12 Months - Unrealized Losses (7) (3)
12 Months or Greater - Fair Value 147 198
12 Months or Greater - Unrealized Losses (5) (1)
Total Fair Value 1,761 1,266
Total Unrealized Losses (12) (4)
Corporate notes and bonds    
Unrealized Losses on Investments [Line Items]    
Less than 12 Months - Fair Value 2,463 669
Less than 12 Months - Unrealized Losses (30) (8)
12 Months or Greater - Fair Value 430 177
12 Months or Greater - Unrealized Losses (13) (4)
Total Fair Value 2,893 846
Total Unrealized Losses (43) (12)
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 19 69
Less than 12 Months - Unrealized Losses 0 (6)
12 Months or Greater - Fair Value 23 148
12 Months or Greater - Unrealized Losses (4) (28)
Total Fair Value 42 217
Total Unrealized Losses $ (4) $ (34)