BUSINESS SEGMENT INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		$ 1,143	$ 1,138	$ 2,282	$ 2,247
Realized investment gains (losses)	[1],[2],[3],[4]	(34)	35	70	(63)
Other income (loss)		0	(42)	(1)	(70)
Earnings before income taxes		1,109	1,131	2,351	2,114
Income taxes applicable to pretax adjusted earnings		297	303	587	592
Effect of foreign currency translation on after tax adjusted earnings		(4)	7	(13)	29
Net interest cash flows from derivatives		(7)		(14)
Gain (loss) on change in fair value of derivative, interest rate component		17	17	33	33
Aflac Japan
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		831	836	1,666	1,654
Hedge costs		62	55	124	110
Aflac U.S.
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		338	340	661	677
Corporate and other
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		(26)	(38)	(45)	(84)
Hedge income		$ 20	$ 7	$ 40	$ 9

[1] A gain of $17 for the three-month periods and $33 for the six-month periods ended June 30, 2019, and 2018, respectively, related to the interest rate component of the change in fair value of foreign currency swaps on notes payable have been reclassified from realized investment gains (losses) and included in adjusted earnings when analyzing operations

[2] Amortized hedge costs of $62 and $55 for the three-month periods and $124 and $110 for the six-month periods ended June 30, 2019, and 2018, respectively, related to certain foreign currency management strategies have been reclassified from realized investment gains (losses) and reported as a deduction from pretax adjusted earnings when analyzing operations.

[3] Amortized hedge income of $20 and $7 for the three-month periods and $40 and $9 for the six-month periods ended June 30, 2019, and 2018, respectively, related to certain foreign currency management strategies has been reclassified from realized investment gains (losses) and reported as an increase in pretax adjusted earnings when analyzing operations.

[4] Net interest cash flows from derivatives associated with certain investment strategies of $(7) for the three-month period and $(14) for the six-month period ended June 30, 2019 and and an immaterial amount for the three- and six-month periods in 2018, respectively, have been reclassified from realized investment gains (losses) and included in adjusted earnings as a component of net investment income.