BUSINESS SEGMENT INFORMATION - Operations by Segment - Revenues (Details) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of reportable insurance business segments | segment				2
Net earned premiums		$ 4,623	$ 4,736	$ 13,969	$ 14,109
Net investment income		896	936	2,669	2,692
Total adjusted revenues		5,535	5,639	16,688	16,703
Net investment gains (losses)	[1],[2],[3],[4]	130	(103)	(454)	1
Total revenues		5,665	5,536	16,234	16,704
Aflac Japan
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		3,168	3,241	9,476	9,593
Adjusted net investment income	[1],[4]	663	659	1,939	1,878
Other income		11	12	32	34
Total revenues		3,842	3,912	11,447	11,505
Hedge costs		51	66	155	191
Net interest cash flows from derivatives		6	(4)	5	(18)
Aflac U.S.
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		1,407	1,445	4,348	4,365
Net investment income	[3]	175	183	523	540
Other income		24	2	78	6
Total revenues		1,606	1,630	4,949	4,911
Net interest cash flows from derivatives		1		2
Corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues	[2]	87	97	292	287
Hedge income		$ 22	$ 21	$ 78	$ 61

[1] 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.

[2] Amortized hedge income of $22 and $21 for the three-month periods $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 to net investment income when analyzing operations.

[3] 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.

[4] 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.