v3.26.1
INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value $ 30,231 $ 28,256
Total Unrealized Losses 6,658 5,924
Less than 12 months Fair Value 11,746 10,656
Less than 12 months Unrealized Losses 515 770
12 months or Longer Fair Value 18,485 17,600
12 months or Longer Unrealized Losses 6,143 5,154
U.S. government and agencies | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 166 37
Total Unrealized Losses 3 2
Less than 12 months Fair Value 130 0
Less than 12 months Unrealized Losses 1 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 12,636 13,521
Total Unrealized Losses 4,099 3,727
Less than 12 months Fair Value 5,083 7,966
Less than 12 months Unrealized Losses 305 692
12 months or Longer Fair Value 7,553 5,555
12 months or Longer Unrealized Losses 3,794 3,035
Municipalities | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 612 630
Total Unrealized Losses 61 54
Less than 12 months Fair Value 92 8
Less than 12 months Unrealized Losses 6 0
12 months or Longer Fair Value 520 622
12 months or Longer Unrealized Losses 55 54
Municipalities | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 487 520
Total Unrealized Losses 163 145
Less than 12 months Fair Value 222 234
Less than 12 months Unrealized Losses 13 6
12 months or Longer Fair Value 265 286
12 months or Longer Unrealized Losses 150 139
Mortgage- and asset-backed securities | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 1,022 547
Total Unrealized Losses 40 35
Less than 12 months Fair Value 674 217
Less than 12 months Unrealized Losses 7 5
12 months or Longer Fair Value 348 330
12 months or Longer Unrealized Losses 33 30
Mortgage- and asset-backed securities | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 314 183
Total Unrealized Losses 43 38
Less than 12 months Fair Value 152 9
Less than 12 months Unrealized Losses 3 1
12 months or Longer Fair Value 162 174
12 months or Longer Unrealized Losses 40 37
Public utilities | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 1,279 1,055
Total Unrealized Losses 127 107
Less than 12 months Fair Value 499 169
Less than 12 months Unrealized Losses 9 2
12 months or Longer Fair Value 780 886
12 months or Longer Unrealized Losses 118 105
Public utilities | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 1,005 838
Total Unrealized Losses 204 174
Less than 12 months Fair Value 211 0
Less than 12 months Unrealized Losses 7 0
12 months or Longer Fair Value 794 838
12 months or Longer Unrealized Losses 197 174
Sovereign and supranational | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 262 276
Total Unrealized Losses 20 13
Less than 12 months Fair Value 224 236
Less than 12 months Unrealized Losses 8 0
12 months or Longer Fair Value 38 40
12 months or Longer Unrealized Losses 12 13
Banks/financial institutions | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 695 252
Total Unrealized Losses 33 21
Less than 12 months Fair Value 534 62
Less than 12 months Unrealized Losses 8 0
12 months or Longer Fair Value 161 190
12 months or Longer Unrealized Losses 25 21
Banks/financial institutions | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 3,439 3,467
Total Unrealized Losses 554 477
Less than 12 months Fair Value 778 495
Less than 12 months Unrealized Losses 54 26
12 months or Longer Fair Value 2,661 2,972
12 months or Longer Unrealized Losses 500 451
Other corporate | U.S. dollar-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 5,644 4,535
Total Unrealized Losses 679 597
Less than 12 months Fair Value 2,158 620
Less than 12 months Unrealized Losses 31 5
12 months or Longer Fair Value 3,486 3,915
12 months or Longer Unrealized Losses 648 592
Other corporate | Yen-denominated    
Investments, Unrealized Loss Position [Line Items]    
Total Fair Value 2,670 2,395
Total Unrealized Losses 632 534
Less than 12 months Fair Value 989 640
Less than 12 months Unrealized Losses 63 33
12 months or Longer Fair Value 1,681 1,755
12 months or Longer Unrealized Losses $ 569 $ 501