BUSINESS SEGMENT INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		$ 1,139	$ 1,109
Realized investment gains (losses)	[1],[2],[3],[4]	103	(98)
Other income (loss)		0	(29)
Earnings before income taxes		1,242	982
Income taxes applicable to pretax adjusted earnings		291	289
Effect of foreign currency translation on after tax adjusted earnings		(8)	21
Net interest cash flows from derivatives		(7)
Gain (loss) on change in fair value of derivative, interest rate component		17	17
Aflac Japan
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		834	818
Hedge costs		62	55
Aflac U.S.
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		323	337
Corporate and other
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		(18)	(46)
Hedge income		$ 20	$ 2

[1] A gain of $17 and $17 for the three-month periods ended March 31, 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 ended March 31, 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 $2 for the three-month periods ended March 31, 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 ended March 31, 2019 and an immaterial amount in 2018, respectively, have been reclassified from realized investment gains (losses) and included in adjusted earnings as a component of net investment income.