v3.26.3
INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - USD ($)
$ in Millions
Sep. 30, 2026
Dec. 31, 2025
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value $ 40,752 $ 28,256
Total Unrealized Losses 7,580 5,924
Less than 12 months Fair Value 23,511 10,656
Less than 12 months Unrealized Losses 1,195 770
12 months or Longer Fair Value 17,241 17,600
12 months or Longer Unrealized Losses 6,385 5,154
U.S. government and agencies | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 154 37
Total Unrealized Losses 7 2
Less than 12 months Fair Value 119 0
Less than 12 months Unrealized Losses 3 0
12 months or Longer Fair Value 35 37
12 months or Longer Unrealized Losses 4 2
Japan government and agencies | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 13,022 13,521
Total Unrealized Losses 3,634 3,727
Less than 12 months Fair Value 6,242 7,966
Less than 12 months Unrealized Losses 271 692
12 months or Longer Fair Value 6,780 5,555
12 months or Longer Unrealized Losses 3,363 3,035
Municipalities | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 656 630
Total Unrealized Losses 118 54
Less than 12 months Fair Value 192 8
Less than 12 months Unrealized Losses 18 0
12 months or Longer Fair Value 464 622
12 months or Longer Unrealized Losses 100 54
Municipalities | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 559 520
Total Unrealized Losses 210 145
Less than 12 months Fair Value 313 234
Less than 12 months Unrealized Losses 33 6
12 months or Longer Fair Value 246 286
12 months or Longer Unrealized Losses 177 139
Mortgage- and asset-backed securities | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 3,415 547
Total Unrealized Losses 166 35
Less than 12 months Fair Value 3,129 217
Less than 12 months Unrealized Losses 124 5
12 months or Longer Fair Value 286 330
12 months or Longer Unrealized Losses 42 30
Mortgage- and asset-backed securities | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 393 183
Total Unrealized Losses 62 38
Less than 12 months Fair Value 233 9
Less than 12 months Unrealized Losses 13 1
12 months or Longer Fair Value 160 174
12 months or Longer Unrealized Losses 49 37
Mortgage- and asset-backed securities | Other currencies    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 57  
Total Unrealized Losses 3  
Less than 12 months Fair Value 57  
Less than 12 months Unrealized Losses 3  
12 months or Longer Fair Value 0  
12 months or Longer Unrealized Losses 0  
Public utilities | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 2,520 1,055
Total Unrealized Losses 268 107
Less than 12 months Fair Value 1,894 169
Less than 12 months Unrealized Losses 114 2
12 months or Longer Fair Value 626 886
12 months or Longer Unrealized Losses 154 105
Public utilities | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 1,433 838
Total Unrealized Losses 279 174
Less than 12 months Fair Value 675 0
Less than 12 months Unrealized Losses 30 0
12 months or Longer Fair Value 758 838
12 months or Longer Unrealized Losses 249 174
Public utilities | Other currencies    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 51  
Total Unrealized Losses 1  
Less than 12 months Fair Value 51  
Less than 12 months Unrealized Losses 1  
12 months or Longer Fair Value 0  
12 months or Longer Unrealized Losses 0  
Sovereign and supranational | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 254 276
Total Unrealized Losses 31 13
Less than 12 months Fair Value 219 236
Less than 12 months Unrealized Losses 16 0
12 months or Longer Fair Value 35 40
12 months or Longer Unrealized Losses 15 13
Banks/financial institutions | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 2,117 252
Total Unrealized Losses 118 21
Less than 12 months Fair Value 1,979 62
Less than 12 months Unrealized Losses 85 0
12 months or Longer Fair Value 138 190
12 months or Longer Unrealized Losses 33 21
Banks/financial institutions | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 3,540 3,467
Total Unrealized Losses 704 477
Less than 12 months Fair Value 662 495
Less than 12 months Unrealized Losses 36 26
12 months or Longer Fair Value 2,878 2,972
12 months or Longer Unrealized Losses 668 451
Other corporate | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 9,561 4,535
Total Unrealized Losses 1,144 597
Less than 12 months Fair Value 6,672 620
Less than 12 months Unrealized Losses 362 5
12 months or Longer Fair Value 2,889 3,915
12 months or Longer Unrealized Losses 782 592
Other corporate | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 3,020 2,395
Total Unrealized Losses 835 534
Less than 12 months Fair Value 1,074 640
Less than 12 months Unrealized Losses 86 33
12 months or Longer Fair Value 1,946 1,755
12 months or Longer Unrealized Losses $ 749 $ 501