BUSINESS SEGMENT INFORMATION - Operations by Segment - Revenues (Details) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) segment	Sep. 30, 2020 USD ($)
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of reportable insurance business segments | segment				2
Net earned premiums		$ 4,372	$ 4,623	$ 13,406	$ 13,969
Total adjusted revenues		5,395	5,535	16,412	16,688
Net investment gains (losses)	[1],[2],[3],[4]	(158)	130	258	(454)
Total revenues		5,237	5,665	16,670	16,234
Aflac Japan
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		2,934	3,168	9,045	9,476
Adjusted net investment income	[1],[3]	763	663	2,260	1,939
Other income		10	11	32	32
Total adjusted revenues		3,707	3,842	11,337	11,447
Hedge costs		20	51	55	155
Net interest cash flows from derivatives		(7)	6	(24)	5
Aflac U.S.
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		1,393	1,407	4,223	4,348
Adjusted net investment income	[4]	191	175	557	523
Other income		32	24	90	78
Total adjusted revenues		1,616	1,606	4,870	4,949
Net interest cash flows from derivatives		1	1	1	2
Corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total adjusted revenues	[2],[5]	72	87	205	292
Hedge income		13	$ 22	45	$ 78
Corporate and Other
Segment Reporting, Revenue Reconciling Item [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] 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.

[2] 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 to net investment income when analyzing operations.

[3] 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.

[4] 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.

[5] 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, are 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.