POLICY LIABILITIES - Summary of Discounted Expected Future Gross Premiums and Expected Future Policy Benefits and Expenses (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025	Dec. 31, 2024
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	$ 95,919	$ 99,697
Benefits and Expenses	95,680	100,522
Aflac Japan \| Cancer
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	34,767	36,796
Benefits and Expenses	32,936	34,987	$ 40,781
Aflac Japan \| Medical and other health
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	20,742	22,239
Benefits and Expenses	16,476	17,692	20,606
Aflac Japan \| Life insurance
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	8,216	8,625
Benefits and Expenses	19,394	20,894	24,265
Aflac Japan \| Other
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	953	1,018
Benefits and Expenses	3,435	3,671	4,225
Aflac U.S. \| Life insurance
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	2,469	2,358
Benefits and Expenses	2,118	2,076	1,847
Aflac U.S. \| Accident
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	5,919	6,002
Benefits and Expenses	3,125	3,184	3,127
Aflac U.S. \| Disability
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	4,435	4,478
Benefits and Expenses	2,322	2,336	2,330
Aflac U.S. \| Critical care
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	11,865	11,988
Benefits and Expenses	10,690	10,845	10,701
Aflac U.S. \| Hospital indemnity
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	3,334	3,333
Benefits and Expenses	1,946	1,955	1,897
Aflac U.S. \| Dental/vision
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	737	755
Benefits and Expenses	434	438	441
Aflac U.S. \| Other
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	2,482	2,105
Benefits and Expenses	$ 2,804	$ 2,444	$ 1,288