Schedule II - Aflac Incorporated (Parent Only) - Condensed Statement of Earnings (Detail) - USD ($)		1 Months Ended	3 Months Ended								12 Months Ended
		Nov. 30, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Income Statements, [Line Items]
Net investment income			$ 812,000,000	$ 811,000,000	$ 802,000,000	$ 794,000,000	$ 813,000,000	$ 842,000,000	$ 822,000,000	$ 801,000,000	$ 3,220,000,000	$ 3,278,000,000	$ 3,135,000,000
Realized investment gains (losses)											(151,000,000)	(14,000,000)	106,000,000
Other income (loss)			17,000,000	17,000,000	17,000,000	17,000,000	20,000,000	16,000,000	15,000,000	18,000,000	67,000,000	70,000,000	61,000,000
Total revenues			5,424,000,000	5,506,000,000	5,428,000,000	5,309,000,000	5,955,000,000	5,716,000,000	5,437,000,000	5,451,000,000	21,667,000,000	22,559,000,000	20,872,000,000
Interest expense											240,000,000	268,000,000	289,000,000
Earnings before income taxes			999,000,000	1,075,000,000	1,045,000,000	898,000,000	1,153,000,000	963,000,000	834,000,000	1,117,000,000	4,018,000,000	4,067,000,000	3,862,000,000
Current tax expense (benefit)											631,000,000	884,000,000	1,288,000,000
Deferred tax expense (benefit)											(1,217,000,000)	524,000,000	41,000,000
Total income tax expense			$ (1,585,000,000)	$ 359,000,000	$ 332,000,000	$ 306,000,000	$ 402,000,000	$ 334,000,000	$ 286,000,000	$ 386,000,000	(586,000,000)	1,408,000,000	1,329,000,000
Net earnings											4,604,000,000	2,659,000,000	2,533,000,000
Parent Company
Condensed Income Statements, [Line Items]
Management and service fees from subsidiaries	[1]										297,000,000	265,000,000	260,000,000
Net investment income											30,000,000	18,000,000	22,000,000
Interest from subsidiaries	[1]										5,000,000	5,000,000	6,000,000
Realized investment gains (losses)											67,000,000	84,000,000	86,000,000
Change in fair value on the cross-currency interest rate swaps											(68,000,000)	(159,000,000)	(53,000,000)
Total revenues											331,000,000	213,000,000	321,000,000
Interest expense											197,000,000	213,000,000	231,000,000
Other operating expenses	[2]										180,000,000	277,000,000	321,000,000
Total operating expenses											377,000,000	490,000,000	552,000,000
Earnings before income taxes											(46,000,000)	(277,000,000)	(231,000,000)
Total income tax expense											(23,000,000)	(102,000,000)	(80,000,000)
Earnings before equity in earnings of subsidiaries											(23,000,000)	(175,000,000)	(151,000,000)
Equity in earnings of subsidiaries	[1],[3]										4,627,000,000	2,834,000,000	2,684,000,000
Net earnings											4,604,000,000	2,659,000,000	2,533,000,000
5.50% subordinated notes due September 2052
Condensed Income Statements, [Line Items]
Expense on extinguishment of debt		$ 13,000,000									$ 13,000,000
Senior Notes due 2039 and 2040
Condensed Income Statements, [Line Items]
Expense on extinguishment of debt												$ 137,000,000
8.50% senior notes due May 2019
Condensed Income Statements, [Line Items]
Expense on extinguishment of debt													$ 230,000,000

[1] Eliminated in consolidation

[2] Includes expense of $13 in 2017, $137 in 2016 and $230 in 2015 for the early extinguishment of debt

[3] Eliminated in consolidation