POLICY LIABILITIES - Schedule of Changes in Present Value of Expected Net Premiums and Expected Future Policy Benefits (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Present value of expected future policy benefits:
Beginning balance		$ 132,131
Ending balance		123,453	$ 132,131
Net liability for future policy benefits		77,867	83,718
Aflac Japan | Cancer
Present value of expected premiums:
Beginning balance		17,509	19,298
Beginning balance at original discount rate		16,452	18,221
Effect of changes in cash flow assumptions			0	$ (165)
Effect of actual variances from expected experience			(46)	(315)
Adjusted beginning of period balance			16,406	17,741
Issuances		229	1,034
Interest accrual		97	412
Net premiums collected	[1]	(369)	(1,564)
Foreign currency translation		(1,041)	(1,170)
Other		0	(1)
Ending balance at original discount rate		15,322	16,452
Effect of changes in discount rate assumptions		895	1,057
Ending balance		16,217	17,509
Present value of expected future policy benefits:
Beginning balance		50,161	54,766
Beginning balance at original discount rate		43,626	47,677
Effect of changes in cash flow assumptions			0	(147)
Effect of actual variances from expected experience			(62)	(385)
Adjusted beginning of period balance			43,564	47,145
Issuances		232	1,059
Interest accrual		343	1,473
Benefit payments		(682)	(2,987)
Foreign currency translation		(2,757)	(3,064)
Other		0	0
Ending balance at original discount rate		40,700	43,626
Effect of changes in discount rate assumptions		5,689	6,535
Ending balance		46,389	50,161
Net liability for future policy benefits		30,172	32,652
Less: reinsurance recoverable		3,829	4,135
Net liability for future policy benefits after reinsurance recoverable		26,343	28,517
Aflac Japan | Medical and other health
Present value of expected premiums:
Beginning balance		14,697	16,714
Beginning balance at original discount rate		14,040	16,195
Effect of changes in cash flow assumptions			0	(470)
Effect of actual variances from expected experience			(52)	(137)
Adjusted beginning of period balance			13,988	15,588
Issuances		103	418
Interest accrual		77	334
Net premiums collected	[1]	(290)	(1,261)
Foreign currency translation		(888)	(1,038)
Other		0	(1)
Ending balance at original discount rate		12,990	14,040
Effect of changes in discount rate assumptions		535	657
Ending balance		13,525	14,697
Present value of expected future policy benefits:
Beginning balance		25,257	27,419
Beginning balance at original discount rate		25,023	27,566
Effect of changes in cash flow assumptions			0	(507)
Effect of actual variances from expected experience			(59)	(154)
Adjusted beginning of period balance			24,964	26,905
Issuances		105	432
Interest accrual		142	608
Benefit payments		(246)	(1,153)
Foreign currency translation		(1,582)	(1,769)
Other		0	0
Ending balance at original discount rate		23,383	25,023
Effect of changes in discount rate assumptions		(52)	234
Ending balance		23,331	25,257
Net liability for future policy benefits		9,806	10,560
Less: reinsurance recoverable		1,407	1,521
Net liability for future policy benefits after reinsurance recoverable		8,399	9,039
Aflac Japan | Life insurance
Present value of expected premiums:
Beginning balance		6,488	7,485
Beginning balance at original discount rate		6,258	7,284
Effect of changes in cash flow assumptions			0	43
Effect of actual variances from expected experience			(19)	(42)
Adjusted beginning of period balance			6,239	7,285
Issuances		58	335
Interest accrual		28	124
Net premiums collected	[1]	(226)	(1,017)
Foreign currency translation		(392)	(469)
Other		0	0
Ending balance at original discount rate		5,707	6,258
Effect of changes in discount rate assumptions		194	230
Ending balance		5,901	6,488
Present value of expected future policy benefits:
Beginning balance		29,731	31,954
Beginning balance at original discount rate		30,256	32,800
Effect of changes in cash flow assumptions			0	65
Effect of actual variances from expected experience			(20)	(51)
Adjusted beginning of period balance			30,236	32,814
Issuances		59	341
Interest accrual		146	625
Benefit payments		(516)	(1,415)
Foreign currency translation		(1,909)	(2,109)
Other		0	0
Ending balance at original discount rate		28,016	30,256
Effect of changes in discount rate assumptions		(767)	(525)
Ending balance		27,249	29,731
Net liability for future policy benefits		21,348	23,243
Less: reinsurance recoverable		0	0
Net liability for future policy benefits after reinsurance recoverable		21,348	23,243
Aflac Japan | Other
Present value of expected premiums:
Beginning balance		1,088	1,256
Beginning balance at original discount rate		1,069	1,242
Effect of changes in cash flow assumptions			0	(12)
Effect of actual variances from expected experience			(5)	(15)
Adjusted beginning of period balance			1,064	1,215
Issuances		5	26
Interest accrual		4	20
Net premiums collected	[1]	(26)	(112)
Foreign currency translation		(66)	(80)
Other		0	0
Ending balance at original discount rate		981	1,069
Effect of changes in discount rate assumptions		14	19
Ending balance		995	1,088
Present value of expected future policy benefits:
Beginning balance		5,178	5,582
Beginning balance at original discount rate		5,444	5,940
Effect of changes in cash flow assumptions			0	(27)
Effect of actual variances from expected experience			(8)	(15)
Adjusted beginning of period balance			5,436	5,898
Issuances		7	32
Interest accrual		23	100
Benefit payments		(55)	(206)
Foreign currency translation		(345)	(380)
Other		0	0
Ending balance at original discount rate		5,066	5,444
Effect of changes in discount rate assumptions		(294)	(266)
Ending balance		4,772	5,178
Net liability for future policy benefits		3,777	4,090
Less: reinsurance recoverable		0	0
Net liability for future policy benefits after reinsurance recoverable		3,777	4,090
Aflac U.S. | Life insurance
Present value of expected premiums:
Beginning balance		853	724
Beginning balance at original discount rate		909	799
Effect of changes in cash flow assumptions			0	61
Effect of actual variances from expected experience			(8)	(25)
Adjusted beginning of period balance			901	835
Issuances		66	181
Interest accrual		9	31
Net premiums collected	[1]	(37)	(137)
Foreign currency translation		0	0
Other		1	(1)
Ending balance at original discount rate		940	909
Effect of changes in discount rate assumptions		(66)	(56)
Ending balance		874	853
Present value of expected future policy benefits:
Beginning balance		1,764	1,526
Beginning balance at original discount rate		1,971	1,778
Effect of changes in cash flow assumptions			0	72
Effect of actual variances from expected experience			(11)	(32)
Adjusted beginning of period balance			1,960	1,818
Issuances		70	185
Interest accrual		19	68
Benefit payments		(29)	(105)
Foreign currency translation		0	0
Other		1	5
Ending balance at original discount rate		2,021	1,971
Effect of changes in discount rate assumptions		(246)	(207)
Ending balance		1,775	1,764
Net liability for future policy benefits		901	911
Less: reinsurance recoverable		15	15
Net liability for future policy benefits after reinsurance recoverable		886	896
Aflac U.S. | Accident
Present value of expected premiums:
Beginning balance		2,488	2,534
Beginning balance at original discount rate		2,630	2,760
Effect of changes in cash flow assumptions			0	(16)
Effect of actual variances from expected experience			(18)	(58)
Adjusted beginning of period balance			2,612	2,686
Issuances		111	323
Interest accrual		26	102
Net premiums collected	[1]	(117)	(473)
Foreign currency translation		0	0
Other		0	(8)
Ending balance at original discount rate		2,632	2,630
Effect of changes in discount rate assumptions		(173)	(142)
Ending balance		2,459	2,488
Present value of expected future policy benefits:
Beginning balance		3,109	3,098
Beginning balance at original discount rate		3,302	3,391
Effect of changes in cash flow assumptions			0	(11)
Effect of actual variances from expected experience			(21)	(75)
Adjusted beginning of period balance			3,281	3,305
Issuances		115	331
Interest accrual		32	127
Benefit payments		(125)	(464)
Foreign currency translation		0	0
Other		0	3
Ending balance at original discount rate		3,303	3,302
Effect of changes in discount rate assumptions		(233)	(193)
Ending balance		3,070	3,109
Net liability for future policy benefits		611	621
Less: reinsurance recoverable		0	0
Net liability for future policy benefits after reinsurance recoverable		611	621
Aflac U.S. | Disability
Present value of expected premiums:
Beginning balance		1,652	1,635
Beginning balance at original discount rate		1,738	1,775
Effect of changes in cash flow assumptions			0	(51)
Effect of actual variances from expected experience			(10)	(29)
Adjusted beginning of period balance			1,728	1,695
Issuances		121	376
Interest accrual		16	62
Net premiums collected	[1]	(99)	(390)
Foreign currency translation		0	0
Other		(1)	(5)
Ending balance at original discount rate		1,765	1,738
Effect of changes in discount rate assumptions		(99)	(86)
Ending balance		1,666	1,652
Present value of expected future policy benefits:
Beginning balance		2,422	2,445
Beginning balance at original discount rate		2,541	2,636
Effect of changes in cash flow assumptions			0	(59)
Effect of actual variances from expected experience			(17)	(59)
Adjusted beginning of period balance			2,524	2,518
Issuances		128	392
Interest accrual		24	96
Benefit payments		(112)	(465)
Foreign currency translation		0	0
Other		0	0
Ending balance at original discount rate		2,564	2,541
Effect of changes in discount rate assumptions		(141)	(119)
Ending balance		2,423	2,422
Net liability for future policy benefits		757	770
Less: reinsurance recoverable		0	0
Net liability for future policy benefits after reinsurance recoverable		757	770
Aflac U.S. | Critical Care
Present value of expected premiums:
Beginning balance		4,074	4,486
Beginning balance at original discount rate		4,416	5,050
Effect of changes in cash flow assumptions			0	(494)
Effect of actual variances from expected experience			(48)	(223)
Adjusted beginning of period balance			4,368	4,333
Issuances		221	493
Interest accrual		43	179
Net premiums collected	[1]	(139)	(580)
Foreign currency translation		0	0
Other		0	(9)
Ending balance at original discount rate		4,493	4,416
Effect of changes in discount rate assumptions		(412)	(342)
Ending balance		4,081	4,074
Present value of expected future policy benefits:
Beginning balance		11,290	11,489
Beginning balance at original discount rate		12,120	12,846
Effect of changes in cash flow assumptions			0	(592)
Effect of actual variances from expected experience			(60)	(271)
Adjusted beginning of period balance			12,060	11,983
Issuances		233	505
Interest accrual		128	524
Benefit payments		(228)	(893)
Foreign currency translation		0	0
Other		1	1
Ending balance at original discount rate		12,194	12,120
Effect of changes in discount rate assumptions		(1,092)	(830)
Ending balance		11,102	11,290
Net liability for future policy benefits		7,021	7,216
Less: reinsurance recoverable		0	0
Net liability for future policy benefits after reinsurance recoverable		7,021	7,216
Aflac U.S. | Hospital Indemnity
Present value of expected premiums:
Beginning balance		1,107	1,220
Beginning balance at original discount rate		1,193	1,365
Effect of changes in cash flow assumptions			0	(142)
Effect of actual variances from expected experience			(14)	(73)
Adjusted beginning of period balance			1,179	1,150
Issuances		95	249
Interest accrual		11	45
Net premiums collected	[1]	(58)	(247)
Foreign currency translation		0	0
Other		(1)	(4)
Ending balance at original discount rate		1,226	1,193
Effect of changes in discount rate assumptions		(99)	(86)
Ending balance		1,127	1,107
Present value of expected future policy benefits:
Beginning balance		1,943	2,074
Beginning balance at original discount rate		2,076	2,300
Effect of changes in cash flow assumptions			0	(194)
Effect of actual variances from expected experience			(18)	(99)
Adjusted beginning of period balance			2,058	2,007
Issuances		99	258
Interest accrual		20	84
Benefit payments		(76)	(274)
Foreign currency translation		0	0
Other		0	1
Ending balance at original discount rate		2,101	2,076
Effect of changes in discount rate assumptions		(163)	(133)
Ending balance		1,938	1,943
Net liability for future policy benefits		811	836
Less: reinsurance recoverable		0	0
Net liability for future policy benefits after reinsurance recoverable		811	836
Aflac U.S. | Dental/Vision
Present value of expected premiums:
Beginning balance		206	211
Beginning balance at original discount rate		217	231
Effect of changes in cash flow assumptions			0	(9)
Effect of actual variances from expected experience			(4)	(17)
Adjusted beginning of period balance			213	205
Issuances		18	44
Interest accrual		2	8
Net premiums collected	[1]	(10)	(39)
Foreign currency translation		0	0
Other		(1)	(1)
Ending balance at original discount rate		222	217
Effect of changes in discount rate assumptions		(14)	(11)
Ending balance		208	206
Present value of expected future policy benefits:
Beginning balance		478	488
Beginning balance at original discount rate		506	532
Effect of changes in cash flow assumptions			0	(14)
Effect of actual variances from expected experience			(5)	(22)
Adjusted beginning of period balance			501	496
Issuances		16	46
Interest accrual		5	21
Benefit payments		(14)	(59)
Foreign currency translation		0	0
Other		1	2
Ending balance at original discount rate		509	506
Effect of changes in discount rate assumptions		(35)	(28)
Ending balance		474	478
Net liability for future policy benefits		266	272
Less: reinsurance recoverable		0	0
Net liability for future policy benefits after reinsurance recoverable		266	272
Aflac U.S. | Other
Present value of expected premiums:
Beginning balance		277	110
Beginning balance at original discount rate		272	118
Effect of changes in cash flow assumptions			0	(9)
Effect of actual variances from expected experience			2	(2)
Adjusted beginning of period balance			274	107
Issuances		147	169
Interest accrual		3	6
Net premiums collected	[1]	(8)	(17)
Foreign currency translation		0	0
Other		(1)	7
Ending balance at original discount rate		415	272
Effect of changes in discount rate assumptions		6	5
Ending balance		421	277
Present value of expected future policy benefits:
Beginning balance		798	622
Beginning balance at original discount rate		769	624
Effect of changes in cash flow assumptions			0	(13)
Effect of actual variances from expected experience			2	(4)
Adjusted beginning of period balance			771	$ 607
Issuances		151	169
Interest accrual		10	33
Benefit payments		(17)	(48)
Foreign currency translation		0	0
Other		0	8
Ending balance at original discount rate		915	769
Effect of changes in discount rate assumptions		15	29
Ending balance		930	798
Net liability for future policy benefits		509	521
Less: reinsurance recoverable		2	0
Net liability for future policy benefits after reinsurance recoverable		$ 507	$ 521

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