BUSINESS SEGMENT INFORMATION - Operations by Segment - Revenues (Details) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($)
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of Reportable Insurance Business Segments | segment				2
Net earned premiums		$ 4,736	$ 4,636	$ 14,109	$ 14,086
Net investment income		936	870	2,692	2,569
Total adjusted revenues		5,639	5,473	16,703	16,557
Realized investment gains (losses)	[1],[2],[3]	(103)	104	1	75
Total revenues		5,536	5,577	16,704	16,632
Aflac Japan
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		3,241	3,159	9,593	9,649
Net investment income, less amortized hedge costs	[1],[3]	659	606	1,878	1,801
Other income		12	10	34	31
Total revenues		3,912	3,775	11,505	11,481
Hedge costs		66	59	191	168
Net interest cash flows from derivatives		(4)		(18)
Aflac U.S.
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		1,445	1,426	4,365	4,280
Net investment income		183	187	540	544
Other income		2	3	6	7
Total revenues		1,630	1,616	4,911	4,831
Corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues	[2]	97	82	287	245
Hedge income		$ 21	$ 9	$ 61	$ 18

[1] Amortized hedge costs of $66 and $59 for the three-month periods and $191 and $168 for the nine-month periods ended September 30, 2019, and 2018, respectively, related to certain foreign currency exposure management strategies have been reclassified from realized investment gains (losses) and reported as a deduction from net investment income when analyzing operations.

[2] Amortized hedge income of $21 and $9 for the three-month periods and $61 and $18 for the nine-month periods ended September 30, 2019, and 2018, respectively, related to certain foreign currency exposure management strategies has been reclassified from realized 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 $(4) for the three-month period and $(18) for the nine-month period ended September 30, 2019 and an immaterial amount for the three- and nine-month periods in 2018, respectively, have been reclassified from realized investment gains (losses) and included in adjusted earnings as a component of net investment income.