BUSINESS SEGMENT INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[1]	$ 1,037	$ 1,156	$ 3,455	$ 3,438
Net investment gains (losses)	[2],[3],[4],[5],[6]	117	(120)	(497)	(49)
Other income (loss)		(1)	0	(16)	(1)
Earnings before income taxes		1,153	1,036	2,942	3,388
Income taxes applicable to pretax adjusted earnings		43	293	659	880
Effect of foreign currency translation on after tax adjusted earnings		3	15	17	2
Interest expense on debt		44	34	122	100
Aflac Japan
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[2],[6]	747	838	2,442	2,504
Hedge costs		51	66	155	191
Net interest cash flows from derivatives		6	(4)	5	(18)
Aflac U.S.
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[5]	329	335	1,082	996
Net interest cash flows from derivatives		1		2
Corporate and other
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[3],[4]	(39)	(17)	(69)	(62)
Hedge income		22	21	78	61
Gain (loss) on change in fair value of derivative, interest rate component		$ 13	$ 16	$ 43	$ 50

[1] Includes $44 and $34 for the three-month periods and $122 and $100 for the nine-month periods ended September 30, 2020, and 2019, respectively, of interest expense on debt.

[2] Amortized hedge costs of $51 and $66 for the three-month periods and $155 and $191 for the nine-month periods ended September 30, 2020, and 2019, respectively, related to certain foreign currency exposure management strategies have been reclassified from net investment gains (losses) and reported as a deduction from net investment income when analyzing operations.

[3] A gain of $13 and $16 for three-month periods and $43 and $50 for the nine-month periods ended September 30, 2020, and 2019, respectively, related to the interest rate component of the change in fair value of foreign currency swaps on notes payable has been reclassified from net investment gains (losses) and included in adjusted earnings when analyzing operations.

[4] Amortized hedge income of $22 and $21 for the three-month periods and $78 and $61 for the nine-month periods ended September 30, 2020, and 2019, respectively, related to certain foreign currency exposure management strategies has been reclassified from net investment gains (losses) and reported as an increase in net investment income when analyzing operations.

[5] Net interest cash flows from derivatives associated with certain investment strategies of $1 for the three-month period and $2 for the nine-month period ended September 30, 2020, respectively, have been reclassified from net investment gains (losses) and included in adjusted earnings as a component of net investment income.

[6] Net interest cash flows from derivatives associated with certain investment strategies of $6 and $(4) for the three-month periods and $5 and $(18) for the nine-month periods ended September 30, 2020 and 2019, respectively, have been reclassified from net investment gains (losses) and included in adjusted earnings as a component of net investment income.