POLICY LIABILITIES - Summary of Undiscounted Expected Future Gross Premiums and Future Benefits and Expenses (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	$ 149,102	$ 142,653
Benefits and Expenses	180,123	173,393
Aflac Japan | Cancer
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	55,514	51,712
Benefits and Expenses	58,013	56,881
Aflac Japan | Medical and other health
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	34,838	33,250
Benefits and Expenses	36,969	34,864
Aflac Japan | Life insurance
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	11,332	10,915
Benefits and Expenses	39,259	37,520
Aflac Japan | Other
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	1,451	1,477
Benefits and Expenses	6,809	6,479
Aflac U.S. | Life insurance
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	3,239	2,966
Benefits and Expenses	3,840	3,559
Aflac U.S. | Accident
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	8,682	8,862
Benefits and Expenses	4,727	4,687
Aflac U.S. | Disability
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	5,720	5,727
Benefits and Expenses	3,039	3,094
Aflac U.S. | Critical Care
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	19,350	19,624
Benefits and Expenses	20,051	20,340
Aflac U.S. | Hospital Indemnity
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	4,819	4,859
Benefits and Expenses	3,043	3,017
Aflac U.S. | Dental/Vision
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	1,091	1,118
Benefits and Expenses	660	679
Aflac U.S. | Other
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	3,066	2,143
Benefits and Expenses	$ 3,713	$ 2,273