POLICY LIABILITIES - Summary of Discounted Expected Future Gross Premiums and Expected Future Policy Benefits and Expenses (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025	Dec. 31, 2024
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	$ 90,180	$ 99,697
Benefits and Expenses	89,295	100,522
Aflac Japan \| Cancer
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	32,407	36,796
Benefits and Expenses	30,092	34,987	$ 40,781
Aflac Japan \| Medical and other health
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	19,438	22,239
Benefits and Expenses	15,449	17,692	20,606
Aflac Japan \| Life insurance
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	7,906	8,625
Benefits and Expenses	18,550	20,894	24,265
Aflac Japan \| Other
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	883	1,018
Benefits and Expenses	3,297	3,671	4,225
Aflac U.S. \| Life insurance
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	2,525	2,358
Benefits and Expenses	2,064	2,076	1,847
Aflac U.S. \| Accident
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	5,509	6,002
Benefits and Expenses	2,965	3,184	3,127
Aflac U.S. \| Disability
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	4,205	4,478
Benefits and Expenses	2,171	2,336	2,330
Aflac U.S. \| Critical care
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	11,056	11,988
Benefits and Expenses	9,772	10,845	10,701
Aflac U.S. \| Hospital indemnity
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	3,151	3,333
Benefits and Expenses	1,790	1,955	1,897
Aflac U.S. \| Dental/vision
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	681	755
Benefits and Expenses	400	438	441
Aflac U.S. \| Other
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	2,419	2,105
Benefits and Expenses	$ 2,745	$ 2,444	$ 1,288