BUSINESS SEGMENT INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[1]	$ 1,183	$ 1,139
Net investment gains (losses)	[2],[3],[4],[5]	(448)	103
Other income (loss)		(15)	0
Earnings before income taxes		720	1,242
Income taxes applicable to pretax adjusted earnings		301	291
Effect of foreign currency translation on after tax adjusted earnings		9	(8)
Interest expense on debt		33	33
Aflac Japan
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[3],[5]	855	834
Hedge costs		55	62
Net interest cash flows from derivatives		(6)	(7)
Aflac U.S.
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		326	323
Corporate and other
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[2],[4]	2	(18)
Hedge income		29	20
Gain (loss) on change in fair value of derivative, interest rate component		$ 16	$ 17

[1] Includes $33 for the three-month periods ended March 31, 2020, and 2019, respectively, of interest expense on debt.

[2] A gain of $16 and $17 for the three-month periods ended March 31, 2020, and 2019, respectively, related to the interest rate component of the change in fair value of foreign currency swaps on notes payable has been reclassified from net investment gains (losses) and included in adjusted earnings when analyzing operations.

[3] 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.

[4] 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 in net investment income when analyzing operations.

[5] 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.