BUSINESS SEGMENT INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		$ 1,138	$ 1,073	$ 2,247	$ 2,100
Realized investment gains (losses)	[1],[2],[3]	35	(19)	(63)	(128)
Other income (loss)		(42)	(9)	(70)	(28)
Earnings before income taxes		1,131	1,045	2,114	1,944
Income taxes applicable to pretax adjusted earnings		303	342	592	694
Effect of foreign currency translation on after tax adjusted earnings		7	(9)	29	(3)
Gain (loss) on change in fair value of derivative, corporate		7		9
Gain (loss) on change in fair value of derivative, interest rate component		17	20	33	41
Aflac Japan
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[2]	836	791	1,654	1,560
Hedge costs		55	56	110	108
Aflac U.S.
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings		340	330	677	640
Corporate and other
Segment Reporting, Reconciling Item for Adjusted Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings	[1]	$ (38)	$ (48)	$ (84)	$ (100)

[1] Amortized hedge costs in Aflac Japan were partially offset by derivatives entered into as part of corporate activities and resulted in a benefit of $7 for the three-month period and $9 for the six-month period ended June 30, 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 $56 for the three- month periods and $110 and $108 for the six-month periods ended June 30, 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 $20 for the three-month periods and $33 and $41 for the six-month periods ended June 30, 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