Schedule II - Aflac Incorporated (Parent Only) - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net earnings		$ 2,920	$ 4,604	$ 2,659
Adjustments to reconcile net earnings to net cash provided from operating activities:
Other, net		571	150	340	[1]
Net cash provided (used) by operating activities		6,014	6,128	5,987
Cash flows from investing activities:
Fixed maturity securities purchased		(9,086)	(9,867)	(10,890)
Other investments sold (purchased)		(414)	(206)	(98)
Settlement of derivatives		(241)	(621)	1,252
Other, net		176	(68)	(76)
Net cash provided (used) by investing activities		(3,582)	(5,431)	(3,855)
Cash flows from financing activities:
Purchases of treasury stock		(1,301)	(1,351)	(1,422)
Proceeds from borrowings		1,020	1,040	986
Principal payments under debt obligations		(550)	(1,161)	(610)
Dividends paid to shareholders		(793)	(661)	(658)
Treasury stock reissued		58	33	46
Proceeds from exercise of stock options		48	58	68
Other, net		(19)	0	(120)	[1]
Net cash provided (used) by financing activities		(1,616)	(2,065)	(1,619)
Net change in cash and cash equivalents		846	(1,368)	509
Cash and cash equivalents, beginning of period		3,491	4,859	4,350
Cash and cash equivalents, end of period		4,337	3,491	4,859
Parent Company
Cash flows from operating activities:
Net earnings		2,920	4,604	2,659
Adjustments to reconcile net earnings to net cash provided from operating activities:
Equity in earnings of subsidiaries	[2]	(3,074)	(4,627)	(2,834)
Cash dividends received from subsidiaries		1,820	2,001	2,020
Other, net		99	(46)	294	[3]
Net cash provided (used) by operating activities		1,765	1,932	2,139
Cash flows from investing activities:
Fixed maturity securities sold		207	263	225
Fixed maturity securities purchased		(254)	(329)	(229)
Other investments sold (purchased)		31	(47)	6
Settlement of derivatives		(2)	223	0
Additional capitalization of subsidiaries	[2]	(62)	(69)	(36)
Other, net		(107)	(218)	(25)
Net cash provided (used) by investing activities		(187)	(177)	(59)
Cash flows from financing activities:
Purchases of treasury stock		(1,301)	(1,351)	(1,422)
Proceeds from borrowings		1,020	1,040	986
Principal payments under debt obligations		(550)	(1,161)	(621)
Dividends paid to shareholders		(793)	(661)	(658)
Treasury stock reissued		58	33	46
Proceeds from exercise of stock options		34	38	36
Net change in amount due to/from subsidiary	[2]	(4)	(5)	(6)
Other, net		0	0	(125)	[3]
Net cash provided (used) by financing activities		(1,536)	(2,067)	(1,764)
Net change in cash and cash equivalents		42	(312)	316
Cash and cash equivalents, beginning of period		1,725	2,037	1,721
Cash and cash equivalents, end of period		$ 1,767	$ 1,725	2,037
Senior Notes due 2039 and 2040
Condensed Cash Flow Statements, Captions [Line Items]
Expense on extinguishment of debt				$ 137

[1] Operating activities excludes and financing activities includes a cash outflow of $137 in 2016 for the payments associated with the early extinguishment of debt

[2] Eliminated in consolidation

[3] Operating activities excludes and financing activities includes a cash outflow of $137 in 2016 for the payment associated with the early extinguishment of debt