SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION - (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	$ 10,128				$ 9,875				$ 10,128	$ 9,875
Future policy benefits & unpaid policy claims	94,994				90,952				94,994	90,952
Unearned premiums	4,243				5,090				4,243	5,090
Other policyholders' funds	7,317				7,146				7,317	7,146
Premiums Earned, Net	4,671	$ 4,736	$ 4,681	$ 4,691	4,591	$ 4,636	$ 4,706	$ 4,745	18,780	18,677	$ 18,531
Net investment income	886	$ 936	$ 878	$ 878	874	$ 870	$ 862	$ 837	3,578	3,442	3,220
Benefits and claims, net									11,942	12,000	12,181
Amortization of deferred policy acquisition costs									1,282	1,245	1,132
Other operating expenses									4,638	4,530	4,336
Premiums written									18,180	18,005	17,657
Aflac Japan
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	6,584				6,384				6,584	6,384	6,150
Future policy benefits & unpaid policy claims	84,341				80,672				84,341	80,672
Unearned premiums	4,135				4,977				4,135	4,977
Other policyholders' funds	7,317				7,145				7,317	7,145
Premiums Earned, Net									12,772	12,762	12,752
Net investment income									2,753	2,639	2,463
Benefits and claims, net									8,877	8,913	9,087
Amortization of deferred policy acquisition costs									709	710	630
Other operating expenses									2,465	2,374	2,257
Premiums written									12,367	12,298	12,092
Aflac U.S.
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	3,544				3,491				3,544	3,491	3,355
Future policy benefits & unpaid policy claims	11,184				10,864				11,184	10,864
Unearned premiums	111				117				111	117
Other policyholders' funds	0				0				0	0
Premiums Earned, Net									5,808	5,708	5,563
Net investment income									720	727	721
Benefits and claims, net									2,871	2,887	2,885
Amortization of deferred policy acquisition costs									573	534	502
Other operating expenses									1,834	1,736	1,658
Premiums written									5,813	5,707	5,565
All other
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	0				0				0	0
Future policy benefits & unpaid policy claims	223				183				223	183
Unearned premiums	0				0				0	0
Other policyholders' funds	0				1				0	1
Premiums Earned, Net									200	207	216
Net investment income									105	76	36
Benefits and claims, net									194	200	209
Amortization of deferred policy acquisition costs									0	1	0
Other operating expenses									339	420	421
Premiums written									0	0	$ 0
Intercompany eliminations
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	0				0				0	0
Future policy benefits & unpaid policy claims	(754)				(767)				(754)	(767)
Unearned premiums	(3)				(4)				(3)	(4)
Other policyholders' funds	$ 0				$ 0				$ 0	$ 0