SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Liability For Future Policy Benefit, Expected Net Premium, Activity (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2021
Cancer | Aflac Japan
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance		$ 19,298	$ 25,893
Beginning balance at original discount rate		18,221	22,470
Effect of changes in cash flow assumptions			(166)	$ (639)
Effect of actual variances from expected experience			(261)	(284)
Adjusted beginning of period balance			17,794	21,547
Issuances		770	947
Interest accrual		312	459
Net premiums collected	[1]	(1,182)	(1,734)
Foreign currency translation		(2,023)	(2,997)
Other		(1)	(1)
Ending balance at original discount rate		15,670	18,221	22,470
Effect of changes in discount rate assumptions		823	1,077
Ending balance		16,493	19,298	25,893
Cancer | Aflac Japan | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance			25,893
Beginning balance at original discount rate			22,470
Effect of changes in cash flow assumptions					$ 32
Effect of actual variances from expected experience					(134)
Adjusted beginning of period balance					25,514
Issuances				1,116
Interest accrual				586
Net premiums collected	[2]			(2,206)
Foreign currency translation				(2,539)
Other				(1)
Ending balance at original discount rate				22,470
Effect of changes in discount rate assumptions				3,423
Ending balance				25,893
Medical and other health | Aflac Japan
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance		16,714	21,174
Beginning balance at original discount rate		16,195	18,681
Effect of changes in cash flow assumptions			(473)	317
Effect of actual variances from expected experience			(90)	61
Adjusted beginning of period balance			15,632	19,059
Issuances		285	639
Interest accrual		255	364
Net premiums collected	[1]	(959)	(1,376)
Foreign currency translation		(1,767)	(2,488)
Other		(1)	(3)
Ending balance at original discount rate		13,445	16,195	18,681
Effect of changes in discount rate assumptions		449	519
Ending balance		13,894	16,714	21,174
Medical and other health | Aflac Japan | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance			21,174
Beginning balance at original discount rate			18,681
Effect of changes in cash flow assumptions					88
Effect of actual variances from expected experience					(449)
Adjusted beginning of period balance					20,915
Issuances				1,132
Interest accrual				439
Net premiums collected	[2]			(1,692)
Foreign currency translation				(2,111)
Other				(2)
Ending balance at original discount rate				18,681
Effect of changes in discount rate assumptions				2,493
Ending balance				21,174
Life insurance | Aflac Japan
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance		7,485	10,847
Beginning balance at original discount rate		7,284	10,064
Effect of changes in cash flow assumptions			44	(494)
Effect of actual variances from expected experience			(34)	(81)
Adjusted beginning of period balance			7,294	9,489
Issuances		267	221
Interest accrual		94	146
Net premiums collected	[1]	(778)	(1,229)
Foreign currency translation		(798)	(1,343)
Other		0	0
Ending balance at original discount rate		6,079	7,284	10,064
Effect of changes in discount rate assumptions		171	201
Ending balance		6,250	7,485	10,847
Life insurance | Aflac Japan | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance			10,847
Beginning balance at original discount rate			10,064
Effect of changes in cash flow assumptions					40
Effect of actual variances from expected experience					(135)
Adjusted beginning of period balance					12,381
Issuances				284
Interest accrual				202
Net premiums collected	[2]			(1,609)
Foreign currency translation				(1,194)
Other				0
Ending balance at original discount rate				10,064
Effect of changes in discount rate assumptions				783
Ending balance				10,847
Life insurance | Aflac U.S.
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance		724	834
Beginning balance at original discount rate		799	780
Effect of changes in cash flow assumptions			61	(1)
Effect of actual variances from expected experience			(9)	(16)
Adjusted beginning of period balance			851	763
Issuances		137	146
Interest accrual		23	27
Net premiums collected	[1]	(101)	(131)
Foreign currency translation		0	0
Other		1	(6)
Ending balance at original discount rate		911	799	780
Effect of changes in discount rate assumptions		(105)	(75)
Ending balance		806	724	834
Life insurance | Aflac U.S. | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance			834
Beginning balance at original discount rate			780
Effect of changes in cash flow assumptions					31
Effect of actual variances from expected experience					34
Adjusted beginning of period balance					770
Issuances				112
Interest accrual				25
Net premiums collected	[2]			(124)
Foreign currency translation				0
Other				(3)
Ending balance at original discount rate				780
Effect of changes in discount rate assumptions				54
Ending balance				834
Other | Aflac Japan
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance		1,256	1,586
Beginning balance at original discount rate		1,242	1,461
Effect of changes in cash flow assumptions			(12)	25
Effect of actual variances from expected experience			(9)	(10)
Adjusted beginning of period balance			1,221	1,476
Issuances		19	62
Interest accrual		15	22
Net premiums collected	[1]	(85)	(123)
Foreign currency translation		(137)	(195)
Other		0	0
Ending balance at original discount rate		1,033	1,242	1,461
Effect of changes in discount rate assumptions		9	14
Ending balance		1,042	1,256	1,586
Other | Aflac Japan | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance			1,586
Beginning balance at original discount rate			1,461
Effect of changes in cash flow assumptions					1
Effect of actual variances from expected experience					(11)
Adjusted beginning of period balance					1,698
Issuances				55
Interest accrual				27
Net premiums collected	[2]			(151)
Foreign currency translation				(167)
Other				(1)
Ending balance at original discount rate				1,461
Effect of changes in discount rate assumptions				125
Ending balance				1,586
Other | Aflac U.S.
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance		110	153
Beginning balance at original discount rate		118	135
Effect of changes in cash flow assumptions			(9)	(12)
Effect of actual variances from expected experience			2	6
Adjusted beginning of period balance			111	129
Issuances		76	0
Interest accrual		4	5
Net premiums collected	[1]	(12)	(17)
Foreign currency translation		0	0
Other		8	1
Ending balance at original discount rate		187	118	135
Effect of changes in discount rate assumptions		(15)	(8)
Ending balance		172	110	153
Other | Aflac U.S. | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance			153
Beginning balance at original discount rate			135
Effect of changes in cash flow assumptions					0
Effect of actual variances from expected experience					(3)
Adjusted beginning of period balance					149
Issuances				0
Interest accrual				6
Net premiums collected	[2]			(19)
Foreign currency translation				0
Other				(1)
Ending balance at original discount rate				135
Effect of changes in discount rate assumptions				18
Ending balance				153
Accident | Aflac U.S.
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance		2,534	3,283
Beginning balance at original discount rate		2,760	2,999
Effect of changes in cash flow assumptions			(16)	(52)
Effect of actual variances from expected experience			(44)	(152)
Adjusted beginning of period balance			2,700	2,795
Issuances		256	355
Interest accrual		77	105
Net premiums collected	[1]	(356)	(496)
Foreign currency translation		0	0
Other		(5)	1
Ending balance at original discount rate		2,672	2,760	2,999
Effect of changes in discount rate assumptions		(283)	(226)
Ending balance		2,389	2,534	3,283
Accident | Aflac U.S. | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance			3,283
Beginning balance at original discount rate			2,999
Effect of changes in cash flow assumptions					(163)
Effect of actual variances from expected experience					(109)
Adjusted beginning of period balance					3,078
Issuances				365
Interest accrual				116
Net premiums collected	[2]			(552)
Foreign currency translation				0
Other				(8)
Ending balance at original discount rate				2,999
Effect of changes in discount rate assumptions				284
Ending balance				3,283
Disability | Aflac U.S.
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance		1,635	1,862
Beginning balance at original discount rate		1,775	1,760
Effect of changes in cash flow assumptions			(51)	5
Effect of actual variances from expected experience			(6)	(43)
Adjusted beginning of period balance			1,718	1,722
Issuances		293	384
Interest accrual		46	57
Net premiums collected	[1]	(292)	(382)
Foreign currency translation		0	0
Other		(6)	(6)
Ending balance at original discount rate		1,759	1,775	1,760
Effect of changes in discount rate assumptions		(162)	(140)
Ending balance		1,597	1,635	1,862
Disability | Aflac U.S. | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance			1,862
Beginning balance at original discount rate			1,760
Effect of changes in cash flow assumptions					(129)
Effect of actual variances from expected experience					(38)
Adjusted beginning of period balance					1,754
Issuances				345
Interest accrual				61
Net premiums collected	[2]			(393)
Foreign currency translation				0
Other				(7)
Ending balance at original discount rate				1,760
Effect of changes in discount rate assumptions				102
Ending balance				1,862
Critical Care | Aflac U.S.
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance		4,486	6,023
Beginning balance at original discount rate		5,050	5,391
Effect of changes in cash flow assumptions			(494)	(38)
Effect of actual variances from expected experience			(154)	(421)
Adjusted beginning of period balance			4,402	4,932
Issuances		397	537
Interest accrual		137	193
Net premiums collected	[1]	(440)	(612)
Foreign currency translation		0	0
Other		(5)	0
Ending balance at original discount rate		4,491	5,050	5,391
Effect of changes in discount rate assumptions		(630)	(564)
Ending balance		3,861	4,486	6,023
Critical Care | Aflac U.S. | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance			6,023
Beginning balance at original discount rate			5,391
Effect of changes in cash flow assumptions					(302)
Effect of actual variances from expected experience					(290)
Adjusted beginning of period balance					5,302
Issuances				552
Interest accrual				210
Net premiums collected	[2]			(665)
Foreign currency translation				0
Other				(8)
Ending balance at original discount rate				5,391
Effect of changes in discount rate assumptions				632
Ending balance				6,023
Hospital Indemnity | Aflac U.S.
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance		1,220	1,467
Beginning balance at original discount rate		1,365	1,380
Effect of changes in cash flow assumptions			(142)	42
Effect of actual variances from expected experience			(48)	(111)
Adjusted beginning of period balance			1,175	1,311
Issuances		203	273
Interest accrual		34	45
Net premiums collected	[1]	(187)	(261)
Foreign currency translation		0	0
Other		(3)	(3)
Ending balance at original discount rate		1,222	1,365	1,380
Effect of changes in discount rate assumptions		(150)	(145)
Ending balance		1,072	1,220	1,467
Hospital Indemnity | Aflac U.S. | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance			1,467
Beginning balance at original discount rate			1,380
Effect of changes in cash flow assumptions					0
Effect of actual variances from expected experience					(32)
Adjusted beginning of period balance					1,344
Issuances				263
Interest accrual				45
Net premiums collected	[2]			(268)
Foreign currency translation				0
Other				(4)
Ending balance at original discount rate				1,380
Effect of changes in discount rate assumptions				87
Ending balance				1,467
Dental/Vision | Aflac U.S.
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance		211	264
Beginning balance at original discount rate		231	241
Effect of changes in cash flow assumptions			(9)	10
Effect of actual variances from expected experience			(13)	(20)
Adjusted beginning of period balance			209	231
Issuances		31	33
Interest accrual		6	9
Net premiums collected	[1]	(30)	(42)
Foreign currency translation		0	0
Other		1	0
Ending balance at original discount rate		217	231	241
Effect of changes in discount rate assumptions		(23)	(20)
Ending balance		$ 194	211	264
Dental/Vision | Aflac U.S. | Accounting Standards Update 2018-12
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance			264
Beginning balance at original discount rate			$ 241
Effect of changes in cash flow assumptions					(26)
Effect of actual variances from expected experience					(14)
Adjusted beginning of period balance					$ 241
Issuances				39
Interest accrual				10
Net premiums collected	[2]			(47)
Foreign currency translation				0
Other				(2)
Ending balance at original discount rate				241
Effect of changes in discount rate assumptions				23
Ending balance				$ 264

[1] Net premiums collected represent the portion of gross premiums collected from policyholders that is used to fund expected future benefit payments.

[2] Net premiums collected represent the portion of gross premiums collected from policyholders that is used to fund expected future benefit payments.