BUSINESS SEGMENT INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		$ 1,061	$ 1,014	$ 3,309	$ 3,114
Realized investment gains (losses)	[1],[2],[3],[4]	88	71	25	(57)
Other income (loss)		(3)	(10)	(73)	(38)
Earnings before income taxes		1,146	1,075	3,261	3,019
Income taxes applicable to pretax adjusted earnings		270	338	862	1,031
Effect of foreign currency translation on after tax adjusted earnings		(1)	(29)	27	(31)
Gain (loss) on change in fair value of derivative, corporate		9		18
Gain (loss) on change in fair value of derivative, interest rate component		17	19	50	60
Aflac Japan
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		756	748	2,411	2,308
Hedge costs		59	60	168	168
Aflac U.S.
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		334	316	1,011	956
Corporate and other
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		$ (29)	$ (50)	$ (113)	$ (150)

[1] Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $59 and $60 for the three- month periods and $168 for both the nine-month periods ended September 30, 2018, and 2017, respectively, and have been reclassified from realized investment gains (losses) and reported as a deduction from pretax adjusted earnings when analyzing segment operations.

[2] Excluding a gain of $17 and $19 for the three-month periods and $50 and $60 for the nine-month periods ended September 30, 2018, and 2017, respectively, related to the interest rate component of the change in fair value of foreign currency swaps on notes payable which is included in adjusted earnings when analyzing segment operations

[3] Amortized hedge costs in Aflac Japan were partially offset by derivatives entered into as part of corporate activities and resulted in a benefit of $9 for the three-month period and $18 for the nine-month period ended September 30, 2018 which has been reclassified from realized investment gains (losses) and reported as an increase in pretax adjusted earnings when analyzing operations.

[4] An immaterial amount of net interest cash flows from derivatives associated with certain investment strategies in the three- and nine-month periods ended September 30, 2018, were reclassified from realized investment gains (losses) into net investment income when analyzing operations.