POLICY LIABILITIES - Schedule of Other Policyholders' Funds by Guaranteed Crediting Rates (Details) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]
Policyholder Account Balance, Weighted Average Crediting Rate		1.50%	1.50%
Aflac Japan | Fixed Annuity
Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]
At Guaranteed Minimum	[1]	$ 5,538	$ 5,939	$ 6,423
Cash Surrender Value	[1]	$ 5,457	$ 5,850
Lower Limit | Aflac Japan | Fixed Annuity
Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]
Guaranteed Minimum Crediting Rates	[1],[2]	0.50%	0.50%
Upper Limit | Aflac Japan | Fixed Annuity
Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]
Guaranteed Minimum Crediting Rates	[1],[2]	2.20%	2.30%

[1] Aflac Japan fixed annuities

[2] Weighted-average crediting rate of 1.5% at March 31, 2024 and December 31, 2023.