SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Reconciliation of Future Policy Benefits (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits	$ 78,448	$ 88,241
Deferred profit liability - limited-payment contracts	1,669	1,740
Deferred profit liability - reinsurance	590	692
Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits			$ 115,964
Deferred profit liability - limited-payment contracts			1,595
Deferred profit liability - reinsurance			859
Corporate and other
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits	2,375	686
Corporate and other | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits			30
Cancer | Aflac Japan
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits	30,716	35,468
Cancer | Aflac Japan | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits			46,854
Medical and other health | Aflac Japan
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits	9,699	10,705
Medical and other health | Aflac Japan | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits			14,847
Life insurance | Aflac Japan
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits	21,678	24,469
Life insurance | Aflac Japan | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits			31,873
Life insurance | Aflac U.S.
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits	802	802
Life insurance | Aflac U.S. | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits			1,009
Other | Aflac Japan
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits	3,814	4,326
Other | Aflac Japan | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits			5,736
Other | Aflac U.S.
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits	480	512
Other | Aflac U.S. | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits			684
Accident | Aflac U.S.
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits	575	564
Accident | Aflac U.S. | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits			666
Disability | Aflac U.S.
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits	754	810
Disability | Aflac U.S. | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits			1,009
Critical Care | Aflac U.S.
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits	6,599	7,003
Critical Care | Aflac U.S. | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits			9,365
Hospital Indemnity | Aflac U.S.
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits	775	854
Hospital Indemnity | Aflac U.S. | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits			1,085
Dental/Vision | Aflac U.S.
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits	$ 256	$ 277
Dental/Vision | Aflac U.S. | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Future policy benefits			$ 352