SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION - (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	$ 10,441				$ 10,128				$ 10,441	$ 10,128
Future policy benefits & unpaid policy claims	102,970				94,994				102,970	94,994
Unearned premiums	3,597				4,243				3,597	4,243
Other policyholders' funds	7,824				7,317				7,824	7,317
Net premium income	4,653	$ 4,623	$ 4,664	$ 4,681	4,671	$ 4,736	$ 4,681	$ 4,691	18,622	18,780	$ 18,677
Net investment income	968	$ 896	$ 870	$ 904	886	$ 936	$ 878	$ 878	3,638	3,578	3,442
Benefits and claims, net									11,796	11,942	12,000
Amortization of deferred policy acquisition costs									1,214	1,282	1,245
Other operating expenses									4,978	4,638	4,530
Premiums written									18,075	18,180	18,005
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	(821)				(754)				(821)	(754)
Unearned premiums	0				(3)				0	(3)
Other policyholders' funds	0				0				0	0
Aflac Japan
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	6,991				6,584				6,991	6,584	6,384
Future policy benefits & unpaid policy claims	91,829				84,341				91,829	84,341
Unearned premiums	3,488				4,135				3,488	4,135
Other policyholders' funds	7,811				7,317				7,811	7,317
Net premium income									12,670	12,772	12,762
Net investment income									2,856	2,753	2,639
Benefits and claims, net									8,851	8,877	8,913
Amortization of deferred policy acquisition costs									644	709	710
Other operating expenses									2,613	2,465	2,374
Premiums written									12,312	12,367	12,298
Aflac U.S.
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	3,450				3,544				3,450	3,544	3,491
Future policy benefits & unpaid policy claims	11,684				11,184				11,684	11,184
Unearned premiums	113				111				113	111
Other policyholders' funds	13				0				13	0
Net premium income									5,758	5,808	5,708
Net investment income									702	720	727
Benefits and claims, net									2,765	2,871	2,887
Amortization of deferred policy acquisition costs									570	573	534
Other operating expenses									1,963	1,834	1,736
Premiums written									5,763	5,813	5,707
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	278				223				278	223
Unearned premiums	(4)				0				(4)	0
Other policyholders' funds	$ 0				$ 0				0	0
Net premium income									194	200	207
Net investment income									80	105	76
Benefits and claims, net									180	194	200
Amortization of deferred policy acquisition costs									0	0	1
Other operating expenses									402	339	420
Premiums written									$ 0	$ 0	$ 0