BUSINESS SEGMENT INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[1]	$ 1,341	$ 1,235	$ 2,648	$ 2,418
Net investment gains (losses)	[2],[3],[4],[5]	85	(166)	388	(614)
Other income (loss)		(53)	1	(59)	(15)
Earnings before income taxes		1,373	1,070	2,977	1,789
Income taxes applicable to pretax adjusted earnings		262	315	510	615
Effect of foreign currency translation on after tax adjusted earnings		(6)	5	7	14
Interest expense on debt		45	44	89	77
Aflac Japan
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[2],[5]	1,004	839	1,891	1,694
Hedge costs		17	50	36	105
Net interest cash flows from derivatives		(9)	6	(17)
Aflac U.S.
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		413	426	859	752
Corporate and other
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[3],[4],[6]	(76)	(30)	(102)	(28)
Hedge income		16	27	33	56
Gain (loss) on change in fair value of derivative, interest rate component		14	$ 14	27	$ 30
Corporate and Other
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Income (loss) from federal historic rehabilitation and solar tax credit investments		(30)
Federal historic rehabilitation and solar tax credits, amount		$ 12		$ 25

[1] Includes $45 and $44 for the three-month periods and $89 and $77 for the six-month periods ended June 30, 2021, and 2020, respectively, of interest expense on debt.

[2] Amortized hedge costs of $17 and $50 for the three-month periods and $36 and $105 for the six-month periods ended June 30, 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 for the three-month periods and $27 and $30 for the six-month periods ended June 30, 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 $16 and $27 for the three-month periods and $33 and $56 for the six-month periods ended June 30, 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 $(9) and $6 for the three-month periods and $(17) and an immaterial amount for the six-month periods ended June 30, 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.

[6] Amortization of federal historic rehabilitation and solar investments in partnerships of $30 for the three- and six-month periods ended June 30, 2021, is included as a reduction to net investment income. Offsetting tax credits on these investments of $12 and $25 for the three- and six-month periods ended June 30, 2021, respectively, have been recorded as an income tax benefit. See Note 3 of the Notes to the Consolidated Financial Statements for additional information on these investments.