BUSINESS SEGMENT INFORMATION - Operations by Segment - Revenues (Details) $ in Millions		3 Months Ended
		Mar. 31, 2021 USD ($) segment	Mar. 31, 2020 USD ($)
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of reportable insurance business segments | segment		2
Net earned premiums		$ 4,593	$ 4,681
Total adjusted revenues		5,552	5,594
Net investment gains (losses)	[1],[2],[3]	317	(432)
Total revenues		5,869	5,162
Aflac Japan
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		3,123	3,150
Adjusted net investment income	[1],[3]	705	642
Other income		13	11
Total adjusted revenues		3,841	3,803
Hedge costs		19	55
Net interest cash flows from derivatives		(8)	(6)
Aflac U.S.
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		1,422	1,483
Adjusted net investment income		176	177
Other income		30	27
Total adjusted revenues		1,628	1,687
Corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total adjusted revenues	[2]	83	104
Hedge income		$ 17	$ 29

[1] Amortized hedge costs of $19 and $55 for the three-month periods ended March 31, 2021, and 2020, 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 $17 and $29 for the three-month periods ended March 31, 2021, and 2020, 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 $(8) and $(6) for the three-month periods ended March 31, 2021 and 2020, respectively, have been reclassified from net investment gains (losses) and included in adjusted earnings as a component of net investment income when analyzing operations.