BUSINESS SEGMENT AND FOREIGN INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings										$ 4,354	$ 4,087	$ 4,117
Realized investment gains (losses)	[1],[2],[3],[4]									(297)	0	87
Other income (loss)	[5]									(74)	(69)	(137)
Earnings before income taxes		$ 722	$ 1,146	$ 1,131	$ 982	$ 999	$ 1,075	$ 1,045	$ 898	3,983	4,018	4,067
Income taxes applicable to pretax adjusted earnings										1,129	1,370	1,426
Effect of foreign currency translation on after tax adjusted earnings										28	(41)	141
Gain (loss) on change in fair value of derivative, corporate										36
Gain (loss) on change in fair value of derivative, interest rate component										67	77	85
Aflac Japan
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings										3,208	3,054	3,148
Hedge cost										236	228	186
Aflac U.S.
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings										1,285	1,245	1,208
Corporate and other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax adjusted earnings										$ (139)	(212)	(239)
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
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

[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 $36 for 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 $236, $228 and $186 for 2018, 2017 and 2016, 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 $67 in 2018, $77 in 2017 and $85 in 2016, 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

[4] An immaterial amount of net interest cash flows from derivatives associated with certain investment strategies in 2018, were reclassified from realized investment gains (losses) into net investment income when analyzing operations.

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