BUSINESS SEGMENT INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[1]	$ 1,293	$ 1,037	$ 3,940	$ 3,455
Net investment gains (losses)	[2],[3],[4],[5],[6]	(172)	117	216	(497)
Other income (loss)		(8)	(1)	(66)	(16)
Earnings before income taxes		1,113	1,153	4,090	2,942
Income taxes applicable to pretax adjusted earnings		262	43	771	659
Effect of foreign currency translation on after tax adjusted earnings		(14)	3	(8)	17
Interest expense on debt		40	44	130	122
Aflac Japan
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[2],[5]	976	747	2,867	2,442
Hedge costs		20	51	55	155
Net interest cash flows from derivatives		(7)	6	(24)	5
Aflac U.S.
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[6]	358	329	1,217	1,082
Net interest cash flows from derivatives		1	1	1	2
Corporate and other
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[3],[4],[7]	(41)	(39)	(144)	(69)
Hedge income		13	22	45	78
Gain (loss) on change in fair value of derivative, interest rate component		14	$ 13	41	$ 43
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		(5)		(35)
Federal historic rehabilitation and solar tax credits, amount		$ 10		$ 35

[1] Includes $40 and $44 for the three-month periods and $130 and $122 for the nine-month periods ended September 30, 2021, and 2020, respectively, of interest expense on debt.

[2] Amortized hedge costs of $20 and $51 for the three-month periods and $55 and $155 for the nine-month periods ended September 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 and $13 for the three-month periods and $41 and $43 for the nine-month periods ended September 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 $13 and $22 for the three-month periods and $45 and $78 for the nine-month periods ended September 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 $(7) and $6 for the three-month periods and $(24) and $5 for the nine-month periods ended September 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] Net interest cash flows from derivatives associated with certain investment strategies of $1 for both three-month periods and $1 and $2 for the nine-month periods ended September 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.

[7] The change in value of federal historic rehabilitation and solar investments in partnerships of $5 and $35 for the three- and nine-month periods ended September 30, 2021, respectively, is included as a reduction to net investment income. Offsetting tax credits on these investments of $10 and $35 for the three- and nine-month periods ended September 30, 2021, respectively, have been recorded as an income tax benefit in the consolidated statement of earnings. See Note 3 of the Notes to the Consolidated Financial Statements for additional information on these investments.