v3.25.2
INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - USD ($)
$ in Millions
Jun. 30, 2025
Dec. 31, 2024
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value $ 32,056 $ 24,301
Total Unrealized Losses 5,223 4,128
Less than 12 months Fair Value 14,482 6,716
Less than 12 months Unrealized Losses 554 197
12 months or Longer Fair Value 17,574 17,585
12 months or Longer Unrealized Losses 4,669 3,931
U.S. government and agencies | Dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 108 106
Total Unrealized Losses 2 3
Less than 12 months Fair Value 73 59
Less than 12 months Unrealized Losses 0 1
12 months or Longer Fair Value 35 47
12 months or Longer Unrealized Losses 2 2
Japan government and agencies | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 11,469 8,136
Total Unrealized Losses 2,935 2,234
Less than 12 months Fair Value 5,838 2,070
Less than 12 months Unrealized Losses 288 57
12 months or Longer Fair Value 5,631 6,066
12 months or Longer Unrealized Losses 2,647 2,177
Municipalities | Dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 650 666
Total Unrealized Losses 85 53
Less than 12 months Fair Value 88 67
Less than 12 months Unrealized Losses 5 3
12 months or Longer Fair Value 562 599
12 months or Longer Unrealized Losses 80 50
Municipalities | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 341 341
Total Unrealized Losses 118 79
Less than 12 months Fair Value 88 96
Less than 12 months Unrealized Losses 9 2
12 months or Longer Fair Value 253 245
12 months or Longer Unrealized Losses 109 77
Mortgage- and asset-backed securities | Dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 1,578 567
Total Unrealized Losses 69 34
Less than 12 months Fair Value 1,182 173
Less than 12 months Unrealized Losses 41 2
12 months or Longer Fair Value 396 394
12 months or Longer Unrealized Losses 28 32
Mortgage- and asset-backed securities | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 214 196
Total Unrealized Losses 30 23
Less than 12 months Fair Value 23 12
Less than 12 months Unrealized Losses 0 0
12 months or Longer Fair Value 191 184
12 months or Longer Unrealized Losses 30 23
Public utilities | Dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 1,911 1,570
Total Unrealized Losses 155 151
Less than 12 months Fair Value 1,045 699
Less than 12 months Unrealized Losses 30 19
12 months or Longer Fair Value 866 871
12 months or Longer Unrealized Losses 125 132
Public utilities | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 1,048 1,020
Total Unrealized Losses 183 108
Less than 12 months Fair Value 211 368
Less than 12 months Unrealized Losses 10 11
12 months or Longer Fair Value 837 652
12 months or Longer Unrealized Losses 173 97
Sovereign and supranational | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 48 47
Total Unrealized Losses 11 8
Less than 12 months Fair Value 0 0
Less than 12 months Unrealized Losses 0 0
12 months or Longer Fair Value 48 47
12 months or Longer Unrealized Losses 11 8
Banks/financial institutions | Dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 1,065 625
Total Unrealized Losses 39 36
Less than 12 months Fair Value 890 376
Less than 12 months Unrealized Losses 16 7
12 months or Longer Fair Value 175 249
12 months or Longer Unrealized Losses 23 29
Banks/financial institutions | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 3,759 3,197
Total Unrealized Losses 420 342
Less than 12 months Fair Value 655 471
Less than 12 months Unrealized Losses 16 22
12 months or Longer Fair Value 3,104 2,726
12 months or Longer Unrealized Losses 404 320
Other corporate | Dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 7,675 6,097
Total Unrealized Losses 738 752
Less than 12 months Fair Value 3,823 2,036
Less than 12 months Unrealized Losses 105 59
12 months or Longer Fair Value 3,852 4,061
12 months or Longer Unrealized Losses 633 693
Other corporate | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 2,190 1,733
Total Unrealized Losses 438 305
Less than 12 months Fair Value 566 289
Less than 12 months Unrealized Losses 34 14
12 months or Longer Fair Value 1,624 1,444
12 months or Longer Unrealized Losses $ 404 $ 291