BUSINESS SEGMENT INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[1]	$ 1,306	$ 1,183
Net investment gains (losses)	[2],[3],[4],[5]	304	(448)
Other income (loss)		(7)	(15)
Earnings before income taxes		1,603	720
Income taxes applicable to pretax adjusted earnings		248	301
Effect of foreign currency translation on after tax adjusted earnings		13	9
Interest expense on debt		45	33
Aflac Japan
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[2],[5]	887	855
Hedge costs		19	55
Net interest cash flows from derivatives		(8)	(6)
Aflac U.S.
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		445	326
Corporate and other
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[3],[4]	(26)	2
Hedge income		17	29
Gain (loss) on change in fair value of derivative, interest rate component		$ 14	$ 16

[1] Includes $45 and $33 for the three-month periods ended March 31, 2021, and 2020, respectively, of interest expense on debt.

[2] 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.

[3] A gain of $14 and $16 for the three-month periods ended March 31, 2021, and 2020, 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.

[4] 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 in net investment income when analyzing operations.

[5] 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.