BUSINESS SEGMENT INFORMATION - Operations by Segment - Revenues (Details) $ in Millions		3 Months Ended
		Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of reportable insurance business segments | segment		2
Net earned premiums		$ 4,681	$ 4,691
Net investment income		904	878
Total adjusted revenues		5,594	5,537
Net investment gains (losses)	[1],[2],[3]	(432)	120
Total revenues		5,162	5,657
Aflac Japan
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		3,150	3,180
Adjusted net investment income	[1],[3]	642	610
Other income		11	12
Total revenues		3,803	3,802
Hedge costs		55	62
Net interest cash flows from derivatives		(6)	(7)
Aflac U.S.
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		1,483	1,461
Net investment income		177	177
Other income		27	2
Total revenues		1,687	1,640
Corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues	[2]	104	95
Hedge income		$ 29	$ 20

[1] Amortized hedge costs of $55 and $62 for the three-month periods ended March 31, 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 $29 and $20 for the three-month periods ended March 31, 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 ended March 31, 2020 and 2019, respectively, have been reclassified from net investment gains (losses) and included in adjusted earnings as a component of net investment income.