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POLICY LIABILITIES - Summary of Net Earned Premiums Recognized (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Liability for Future Policy Benefit, Activity [Line Items]        
Reinsurance ceded $ (140) $ (92) $ (411) $ (271)
Net earned premiums [1] 3,304 3,372 9,866 10,223
Aflac Japan | Cancer        
Liability for Future Policy Benefit, Activity [Line Items]        
Gross premiums 720 850 2,332 2,574
Aflac Japan | Medical and other health        
Liability for Future Policy Benefit, Activity [Line Items]        
Gross premiums 474 535 1,443 1,621
Aflac Japan | Life insurance        
Liability for Future Policy Benefit, Activity [Line Items]        
Gross premiums 342 281 932 925
Aflac Japan | Other        
Liability for Future Policy Benefit, Activity [Line Items]        
Gross premiums 30 34 87 99
Aflac U.S. | Life insurance        
Liability for Future Policy Benefit, Activity [Line Items]        
Gross premiums 204 171 598 510
Aflac U.S. | Accident        
Liability for Future Policy Benefit, Activity [Line Items]        
Gross premiums 299 305 907 925
Aflac U.S. | Disability        
Liability for Future Policy Benefit, Activity [Line Items]        
Gross premiums 372 349 1,118 1,055
Aflac U.S. | Critical care        
Liability for Future Policy Benefit, Activity [Line Items]        
Gross premiums 437 439 1,322 1,323
Aflac U.S. | Hospital indemnity        
Liability for Future Policy Benefit, Activity [Line Items]        
Gross premiums 179 181 544 548
Aflac U.S. | Dental/vision        
Liability for Future Policy Benefit, Activity [Line Items]        
Gross premiums 59 52 173 153
Aflac U.S. | Other        
Liability for Future Policy Benefit, Activity [Line Items]        
Gross premiums 76 53 211 143
Corporate and other        
Liability for Future Policy Benefit, Activity [Line Items]        
Gross premiums $ 252 $ 214 $ 610 $ 618
[1] Includes a gain (loss) of $52 and $(55) for the three-month periods and $52 and $(55) for the nine-month periods ended September 30, 2026 and 2025, respectively, related to remeasurement of the deferred profit liability for limited-payment contracts.