POLICY LIABILITIES - Summary of Discounted Expected Future Gross Premiums and Future Benefits and Expenses (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024	Dec. 31, 2023
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	$ 108,491	$ 105,686
Benefits and Expenses	113,560	111,508
Aflac Japan \| Cancer
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	41,068	40,170
Benefits and Expenses	41,726	40,781	$ 50,161
Aflac Japan \| Medical and other health
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	25,563	25,171
Benefits and Expenses	20,664	20,606	25,257
Aflac Japan \| Life insurance
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	9,791	9,367
Benefits and Expenses	24,451	24,265	29,731
Aflac Japan \| Other
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	1,222	1,204
Benefits and Expenses	4,255	4,225	5,178
Aflac U.S. \| Life insurance
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	2,215	2,050
Benefits and Expenses	1,980	1,847	1,764
Aflac U.S. \| Accident
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	6,100	6,057
Benefits and Expenses	3,154	3,127	3,109
Aflac U.S. \| Disability
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	4,462	4,404
Benefits and Expenses	2,367	2,330	2,422
Aflac U.S. \| Critical Care
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	12,147	11,900
Benefits and Expenses	10,942	10,701	11,290
Aflac U.S. \| Hospital Indemnity
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	3,403	3,312
Benefits and Expenses	1,947	1,897	1,943
Aflac U.S. \| Dental/Vision
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	768	761
Benefits and Expenses	452	441	478
Aflac U.S. \| Other
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	1,752	1,290
Benefits and Expenses	$ 1,622	$ 1,288	$ 798