SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION - (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	$ 9,875				$ 9,505				$ 9,875	$ 9,505
Future policy benefits & unpaid policy claims	90,952				86,249				90,952	86,249
Unearned premiums	5,090				5,959				5,090	5,959
Other policyholders' funds	7,146				6,939				7,146	6,939
Premiums Earned, Net	4,591	$ 4,636	$ 4,706	$ 4,745	4,580	$ 4,648	$ 4,665	$ 4,638	18,677	18,531	$ 19,225
Net investment income	874	$ 870	$ 862	$ 837	812	$ 811	$ 802	$ 794	3,442	3,220	3,278
Benefits and claims, net									12,000	12,181	12,919
Amortization of deferred policy acquisition costs									1,245	1,132	1,141
Other operating expenses									4,530	4,336	4,432
Premiums written									18,005	17,657	18,214
Aflac Japan
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	6,384				6,150				6,384	6,150	5,765
Future policy benefits & unpaid policy claims	80,672				76,353				80,672	76,353
Unearned premiums	4,977				5,840				4,977	5,840
Other policyholders' funds	7,145				6,939				7,145	6,939
Premiums Earned, Net									12,762	12,752	13,537
Net investment income									2,639	2,463	2,554
Benefits and claims, net									8,913	9,087	9,828
Amortization of deferred policy acquisition costs									710	630	644
Other operating expenses									2,374	2,257	2,326
Premiums written									12,298	12,092	12,762
Aflac U.S.
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	3,491				3,355				3,491	3,355	3,228
Future policy benefits & unpaid policy claims	10,864				10,506				10,864	10,506
Unearned premiums	117				119				117	119
Other policyholders' funds	0				0				0	0
Premiums Earned, Net									5,708	5,563	5,454
Net investment income									727	721	703
Benefits and claims, net									2,887	2,885	2,869
Amortization of deferred policy acquisition costs									534	502	497
Other operating expenses									1,736	1,658	1,593
Premiums written									5,707	5,565	5,452
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	183				138				183	138
Unearned premiums	0				0				0	0
Other policyholders' funds	1				0				1	0
Premiums Earned, Net									207	216	234
Net investment income									76	36	21
Benefits and claims, net									200	209	222
Amortization of deferred policy acquisition costs									1	0	0
Other operating expenses									420	421	513
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	(767)				(748)				(767)	(748)
Unearned premiums	(4)				0				(4)	0
Other policyholders' funds	$ 0				$ 0				$ 0	$ 0