BUSINESS SEGMENT INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings		$ 1,014	$ 1,092	$ 3,114	$ 3,213
Realized investment gains (losses), non-operating	[1],[2],[3],[4],[5],[6]	71	(130)	(57)	(298)
Other non-operating income (loss)	[5]	(10)	1	(38)	(1)
Earnings before income taxes		1,075	963	3,019	2,914
Income taxes applicable to pretax operating earnings		338	379	1,031	1,112
Effect of foreign currency translation on after tax operating earnings		(29)	61	(31)	110
Gain (loss) on change in fair value of derivative, interest rate component, operating		19	20	60	64
Aflac Japan
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings	[2]	748	827	2,308	2,436
Hedge costs		60	54	168	123
Aflac U.S.
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings		316	323	956	946
Other business segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings		5	4	9	12
Total Business Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings		1,069	1,154	3,273	3,394
Interest expense, noninsurance operations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings		(30)	(31)	(89)	(90)
Corporate and eliminations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings		$ (25)	$ (31)	$ (70)	$ (91)

[1] Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $60 and $54 for the three-month periods and $168 and $123 for the nine-month periods ended September 30, 2017, and 2016, respectively, and have been reclassified from realized investment gains (losses) and reported as a deduction from net investment income when analyzing segment operations to conform to current year reporting.

[2] Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $60 and $54 for the three-month periods and $168 and $123 for the nine-month periods ended September 30, 2017, and 2016, respectively, and have been reclassified from realized investment gains (losses) and reported as a deduction from pretax operating earnings when analyzing segment operations to conform to current year reporting.

[3] Excluding a gain of $19 and $20 for the three-month periods and $60 and $64 for the nine-month periods ended September 30, 2017, and 2016, respectively, related to the interest rate component of the change in fair value of foreign currency swaps on notes payable which is classified as an operating gain when analyzing segment operations

[4] Excluding a gain of $19 and $20 for the three-month periods and $60 and $64 for the nine-month periods ended September 30, 2017, and 2016, respectively, related to the interest rate component of the change in fair value of foreign currency swaps on notes payable which is classified as an operating gain when analyzing segment operations

[5] Prior year foreign currency transaction gains and losses have been reclassified from other non-operating income (loss) to realized investment gains (losses) to conform to current-year reporting classifications. These reclassifications had no impact on total earnings before income taxes.

[6] Prior year foreign currency transaction gains and losses have been reclassified from other non-operating income (loss) to realized investment gains (losses) to conform to current-year reporting classifications. These reclassifications had no impact on total revenues