BUSINESS SEGMENT INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings		$ 1,073	$ 1,042	$ 2,100	$ 2,119
Realized investment gains (losses), non-operating	[1],[2],[3],[4],[5],[6]	(19)	(208)	(128)	(168)
Other non-operating income (loss)	[5]	(9)	0	(28)	0
Earnings before income taxes		1,045	834	1,944	1,951
Income taxes applicable to pretax operating earnings		342	359	694	731
Effect of foreign currency translation on after tax operating earnings		(9)	36	(3)	49
Gain (loss) on change in fair value of derivative, interest rate component, operating		20	21	41	43
Aflac Japan
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings	[2]	791	802	1,560	1,608
Hedge costs		56	37	108	69
Aflac U.S.
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings		330	291	640	623
Other business segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings		3	5	3	8
Total Business Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings		1,124	1,098	2,203	2,239
Interest expense, noninsurance operations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings		(30)	(30)	(59)	(59)
Corporate and eliminations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings		$ (21)	$ (26)	$ (44)	$ (61)

[1] Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $56 and $37 for the three-month periods and $108 and $69 for the six-month periods ended June 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 $56 and $37 for the three-month periods and $108 and $69 for the six-month periods ended June 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 $20 and $21 for the three-month periods and $41 and $43 for the six-month periods ended June 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 $20 and $21 for the three-month periods and $41 and $43 for the six-month periods ended June 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