Schedule II - Aflac Incorporated (Parent Only) - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net earnings		$ 3,304	$ 2,920	$ 4,604
Adjustments to reconcile net earnings to net cash provided from operating activities:
Other, net		358	571	150
Net cash provided (used) by operating activities		5,455	6,014	6,128
Cash flows from investing activities:
Fixed maturity securities purchased		(6,934)	(9,086)	(9,867)
Other investments sold (purchased)		(653)	(414)	(206)
Settlement of derivatives		(9)	(241)	(621)
Other, net		(123)	176	(68)
Net cash provided (used) by investing activities		(3,171)	(3,582)	(5,431)
Cash flows from financing activities:
Purchases of treasury stock		(1,627)	(1,301)	(1,351)
Proceeds from borrowings		615	1,020	1,040
Principal payments under debt obligations		0	(550)	(1,161)
Dividends paid to shareholders		(771)	(793)	(661)
Treasury stock reissued		49	58	33
Proceeds from exercise of stock options		40	48	58
Other, net		22	(19)	0
Net cash provided (used) by financing activities		(1,713)	(1,616)	(2,065)
Net change in cash and cash equivalents		559	846	(1,368)
Cash and cash equivalents, beginning of period		4,337	3,491	4,859
Cash and cash equivalents, end of period		4,896	4,337	3,491
Parent Company
Cash flows from operating activities:
Net earnings		3,304	2,920	4,604
Adjustments to reconcile net earnings to net cash provided from operating activities:
Equity in earnings of subsidiaries	[1]	(3,373)	(3,074)	(4,627)
Cash dividends received from subsidiaries		3,466	1,820	2,001
Other, net		(203)	99	(46)
Net cash provided (used) by operating activities		3,194	1,765	1,932
Cash flows from investing activities:
Fixed maturity securities sold		340	207	263
Fixed maturity securities purchased		(639)	(254)	(329)
Other investments sold (purchased)		(16)	31	(47)
Settlement of derivatives		22	(2)	223
Additional capitalization of subsidiaries	[1]	(214)	(62)	(69)
Other, net		87	(107)	(218)
Net cash provided (used) by investing activities		(420)	(187)	(177)
Cash flows from financing activities:
Purchases of treasury stock		(1,627)	(1,301)	(1,351)
Proceeds from borrowings		347	1,020	1,040
Principal payments under debt obligations		0	(550)	(1,161)
Dividends paid to shareholders		(771)	(793)	(661)
Treasury stock reissued		49	58	33
Proceeds from exercise of stock options		29	34	38
Net change in amount due to/from subsidiary	[1]	(58)	(4)	(5)
Other, net		(2)	0	0
Net cash provided (used) by financing activities		(2,033)	(1,536)	(2,067)
Net change in cash and cash equivalents		741	42	(312)
Cash and cash equivalents, beginning of period		1,767	1,725	2,037
Cash and cash equivalents, end of period		$ 2,508	$ 1,767	$ 1,725

[1] Eliminated in consolidation