Schedule II - Aflac Incorporated (Parent Only) - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net earnings		$ 4,778	$ 3,304	$ 2,920
Adjustments to reconcile net earnings to net cash provided from operating activities:
Other, net		182	358	571
Net cash provided (used) by operating activities		5,958	5,455	6,014
Cash flows from investing activities:
Fixed maturity securities purchased		(4,772)	(6,934)	(9,086)
Other investments sold (purchased)		(860)	(653)	(414)
Settlement of derivatives		18	(9)	(241)
Other, net		(265)	(123)	176
Net cash provided (used) by investing activities		(4,619)	(3,171)	(3,582)
Cash flows from financing activities:
Purchases of treasury stock		(1,537)	(1,627)	(1,301)
Proceeds from borrowings		1,545	615	1,020
Principal payments under debt obligations		(350)	0	(550)
Dividends paid to shareholders		(769)	(771)	(793)
Treasury stock reissued		34	49	58
Proceeds from exercise of stock options		18	40	48
Other, net		(27)	22	(19)
Net cash provided (used) by financing activities		(1,115)	(1,713)	(1,616)
Net change in cash and cash equivalents		245	559	846
Cash and cash equivalents		5,141	4,896
Parent Company
Cash flows from operating activities:
Net earnings		4,778	3,304	2,920
Adjustments to reconcile net earnings to net cash provided from operating activities:
Equity in earnings of subsidiaries	[1]	(4,666)	(3,373)	(3,074)
Cash dividends received from subsidiaries		2,060	3,466	1,820
Other, net		(331)	(203)	99
Net cash provided (used) by operating activities		1,841	3,194	1,765
Cash flows from investing activities:
Fixed maturity securities sold		438	340	207
Fixed maturity securities purchased		(484)	(639)	(254)
Other investments sold (purchased)		(711)	(16)	31
Settlement of derivatives		4	22	(2)
Additional capitalization of subsidiaries	[1]	(291)	(214)	(62)
Other, net		2	87	(107)
Net cash provided (used) by investing activities		(1,042)	(420)	(187)
Cash flows from financing activities:
Purchases of treasury stock		(1,537)	(1,627)	(1,301)
Proceeds from borrowings		1,545	347	1,020
Principal payments under debt obligations		(350)	0	(550)
Dividends paid to shareholders		(769)	(771)	(793)
Treasury stock reissued		34	49	58
Proceeds from exercise of stock options		12	29	34
Net change in amount due to/from subsidiary	[1]	(89)	(58)	(4)
Other, net		(27)	(2)	0
Net cash provided (used) by financing activities		(1,181)	(2,033)	(1,536)
Net change in cash and cash equivalents		(382)	741	42
Cash and cash equivalents		$ 2,126	$ 2,508	$ 1,767	$ 1,725

[1] Eliminated in consolidation