BUSINESS SEGMENT INFORMATION - Operations by Segment - Revenues (Details) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) segment	Jun. 30, 2020 USD ($)
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of reportable insurance business segments | segment				2
Net earned premiums		$ 4,441	$ 4,664	$ 9,034	$ 9,346
Total adjusted revenues		5,466	5,559	11,017	11,153
Net investment gains (losses)	[1],[2],[3]	98	(152)	416	(584)
Total revenues		5,564	5,407	11,433	10,569
Aflac Japan
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		2,987	3,158	6,111	6,308
Adjusted net investment income	[1],[3]	792	633	1,497	1,276
Other income		10	12	22	22
Total adjusted revenues		3,789	3,803	7,630	7,606
Hedge costs		17	50	36	105
Net interest cash flows from derivatives		(9)	6	(17)
Aflac U.S.
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		1,408	1,458	2,830	2,941
Adjusted net investment income		189	172	366	348
Other income		30	26	58	54
Total adjusted revenues		1,627	1,656	3,254	3,343
Corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total adjusted revenues	[2],[4]	50	100	133	204
Hedge income		16	$ 27	33	$ 56
Corporate and Other
Segment Reporting, Revenue Reconciling Item [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] 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.

[2] 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 to net investment income when analyzing operations.

[3] 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.

[4] Amortization of federal historic rehabilitation and solar investments in partnerships of $30 for the three- and six-month periods ended June 30, 2021, are 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 on the consolidated statement of earnings. See Note 3 of the Notes to the Consolidated Financial Statements for additional information on these investments.