BUSINESS SEGMENT INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		$ 1,109	$ 1,027
Realized investment gains (losses)	[1],[2],[3]	(98)	(109)
Other income (loss)		(29)	(20)
Earnings before income taxes		982	898
Income taxes applicable to pretax adjusted earnings		289	351
Effect of foreign currency translation on after tax adjusted earnings		21	5
Gain (loss) on change in fair value of derivative, corporate		2
Gain (loss) on change in fair value of derivative, interest rate component		17	21
Aflac Japan
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[2]	818	769
Hedge costs		55	52
Aflac U.S.
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		337	310
Corporate and other
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[1]	$ (46)	$ (52)

[1] Amortized hedge costs in Aflac Japan were offset by derivatives entered into as part of corporate activities and resulted in a benefit of $2 for the three-month period ended March 31, 2018 which has been reclassified from realized investment gains (losses) and reported as an increase in pretax adjusted earnings when analyzing operations.

[2] Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $55 and $52 for the three-month periods ended March 31, 2018, and 2017, respectively, and have been reclassified from realized investment gains (losses) and reported as a deduction from pretax adjusted earnings when analyzing segment operations.

[3] Excluding a gain of $17 and $21 for the three-month periods ended March 31, 2018, and 2017, respectively, related to the interest rate component of the change in fair value of foreign currency swaps on notes payable which is included in adjusted earnings when analyzing segment operations