BUSINESS SEGMENT AND FOREIGN INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended								12 Months Ended
		Nov. 30, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings											$ 4,087	$ 4,117	$ 4,001
Realized investment gains (losses), non-operating	[1],[2],[3],[4]										0	87	94
Other non-operating income (loss)	[3],[5]										(69)	(137)	(233)
Earnings before income taxes			$ 999	$ 1,075	$ 1,045	$ 898	$ 1,153	$ 963	$ 834	$ 1,117	4,018	4,067	3,862
Income taxes applicable to pretax operating earnings											1,370	1,426	1,377
Effect of foreign currency translation on after tax operating earnings											(41)	141	(198)
Gain (loss) on change in fair value of derivative, interest rate component, operating											77	85	85
Aflac Japan
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Hedge cost											228	186	72
Pretax operating earnings	[1]										3,054	3,148	3,103
Aflac U.S.
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings											1,245	1,208	1,101
Other business segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings											11	18	14
Total Business Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings											4,310	4,374	4,218
Interest expense, noninsurance operations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings											(122)	(128)	(146)
Corporate and eliminations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings											(101)	(129)	(71)
5.50% subordinated notes due September 2052
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Expense on extinguishment of debt		$ 13									$ 13
Senior Notes due 2039 and 2040
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Expense on extinguishment of debt												$ 137
8.50% senior notes due May 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Expense on extinguishment of debt													$ 230

[1] Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $228, $186 and $72 for 2017, 2016 and 2015 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.

[2] Excluding a gain of $77 in 2017 and $85 in both 2016 and 2015 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

[3] 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.

[4] 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.

[5] Includes expense of $13 in 2017, $137 in 2016 and $230 in 2015 for the early extinguishment of debt