BUSINESS SEGMENT INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[1]	$ 1,235	$ 1,143	$ 2,418	$ 2,282
Net investment gains (losses)	[2],[3],[4],[5]	(166)	(34)	(614)	70
Other income (loss)		1	0	(15)	(1)
Earnings before income taxes		1,070	1,109	1,789	2,351
Income taxes applicable to pretax adjusted earnings		315	297	615	587
Effect of foreign currency translation on after tax adjusted earnings		5	(4)	14	(13)
Interest expense on debt		44	34	77	66
Aflac Japan
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[3],[5]	839	831	1,694	1,666
Hedge costs		50	62	105	124
Net interest cash flows from derivatives		6	(7)		(14)
Aflac U.S.
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		426	338	752	661
Corporate and other
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[2],[4]	(30)	(26)	(28)	(45)
Hedge income		27	20	56	40
Gain (loss) on change in fair value of derivative, interest rate component		$ 14	$ 17	$ 30	$ 33

[1] Includes $44 and $34 for the three-month periods and $77 and $66 for the six-month periods ended June 30, 2020, and 2019, respectively, of interest expense on debt.

[2] A gain of $14 and $17 for three-month periods and $30 and $33 for the six-month periods ended June 30, 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 $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.

[4] Amortized hedge income of $27 and $20 for the three-month periods and $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 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 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.