v3.26.1
INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - USD ($)
$ in Millions
Jun. 30, 2026
Dec. 31, 2025
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value $ 28,991 $ 28,256
Total Unrealized Losses 6,631 5,924
Less than 12 months Fair Value 10,916 10,656
Less than 12 months Unrealized Losses 361 770
12 months or Longer Fair Value 18,075 17,600
12 months or Longer Unrealized Losses 6,270 5,154
U.S. government and agencies | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 168 37
Total Unrealized Losses 4 2
Less than 12 months Fair Value 132 0
Less than 12 months Unrealized Losses 2 0
12 months or Longer Fair Value 36 37
12 months or Longer Unrealized Losses 2 2
Japan government and agencies | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 11,520 13,521
Total Unrealized Losses 4,047 3,727
Less than 12 months Fair Value 4,124 7,966
Less than 12 months Unrealized Losses 173 692
12 months or Longer Fair Value 7,396 5,555
12 months or Longer Unrealized Losses 3,874 3,035
Municipalities | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 623 630
Total Unrealized Losses 45 54
Less than 12 months Fair Value 98 8
Less than 12 months Unrealized Losses 5 0
12 months or Longer Fair Value 525 622
12 months or Longer Unrealized Losses 40 54
Municipalities | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 550 520
Total Unrealized Losses 183 145
Less than 12 months Fair Value 302 234
Less than 12 months Unrealized Losses 21 6
12 months or Longer Fair Value 248 286
12 months or Longer Unrealized Losses 162 139
Mortgage- and asset-backed securities | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 1,277 547
Total Unrealized Losses 45 35
Less than 12 months Fair Value 962 217
Less than 12 months Unrealized Losses 12 5
12 months or Longer Fair Value 315 330
12 months or Longer Unrealized Losses 33 30
Mortgage- and asset-backed securities | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 333 183
Total Unrealized Losses 51 38
Less than 12 months Fair Value 169 9
Less than 12 months Unrealized Losses 8 1
12 months or Longer Fair Value 164 174
12 months or Longer Unrealized Losses 43 37
Public utilities | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 1,286 1,055
Total Unrealized Losses 116 107
Less than 12 months Fair Value 602 169
Less than 12 months Unrealized Losses 8 2
12 months or Longer Fair Value 684 886
12 months or Longer Unrealized Losses 108 105
Public utilities | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 1,051 838
Total Unrealized Losses 225 174
Less than 12 months Fair Value 289 0
Less than 12 months Unrealized Losses 12 0
12 months or Longer Fair Value 762 838
12 months or Longer Unrealized Losses 213 174
Sovereign and supranational | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 254 276
Total Unrealized Losses 22 13
Less than 12 months Fair Value 219 236
Less than 12 months Unrealized Losses 9 0
12 months or Longer Fair Value 35 40
12 months or Longer Unrealized Losses 13 13
Banks/financial institutions | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 702 252
Total Unrealized Losses 27 21
Less than 12 months Fair Value 553 62
Less than 12 months Unrealized Losses 5 0
12 months or Longer Fair Value 149 190
12 months or Longer Unrealized Losses 22 21
Banks/financial institutions | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 3,335 3,467
Total Unrealized Losses 599 477
Less than 12 months Fair Value 611 495
Less than 12 months Unrealized Losses 34 26
12 months or Longer Fair Value 2,724 2,972
12 months or Longer Unrealized Losses 565 451
Other corporate | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 5,187 4,535
Total Unrealized Losses 583 597
Less than 12 months Fair Value 2,022 620
Less than 12 months Unrealized Losses 24 5
12 months or Longer Fair Value 3,165 3,915
12 months or Longer Unrealized Losses 559 592
Other corporate | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 2,705 2,395
Total Unrealized Losses 684 534
Less than 12 months Fair Value 833 640
Less than 12 months Unrealized Losses 48 33
12 months or Longer Fair Value 1,872 1,755
12 months or Longer Unrealized Losses $ 636 $ 501