BUSINESS SEGMENT INFORMATION - Operations by Segment - Revenues (Details) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of reportable insurance business segments | segment				2
Net earned premiums		$ 4,664	$ 4,681	$ 9,346	$ 9,373
Net investment income		870	878	1,774	1,756
Total adjusted revenues		5,559	5,528	11,153	11,065
Net investment gains (losses)	[1],[2],[3]	(152)	(17)	(584)	103
Total revenues		5,407	5,511	10,569	11,168
Aflac Japan
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		3,158	3,172	6,308	6,352
Adjusted net investment income	[1],[3]	633	609	1,276	1,219
Other income		12	11	22	22
Total revenues		3,803	3,792	7,606	7,593
Hedge costs		50	62	105	124
Net interest cash flows from derivatives		6	(7)		(14)
Aflac U.S.
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		1,458	1,459	2,941	2,920
Net investment income		172	180	348	357
Other income		26	2	54	4
Total revenues		1,656	1,641	3,343	3,281
Corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues	[2]	100	95	204	191
Hedge income		$ 27	$ 20	$ 56	$ 40

[1] Amortized hedge costs of $50 and $62 for the three-month periods and $105 and $124 for the six-month periods ended June 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 $27 and $20 for the three-month periods $56 and $40 for the six-month periods ended June 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 $6 and $(7) for the three-month periods and an immaterial amount and $(14) for the six-month periods ended June 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.