POLICY LIABILITIES - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liability for Future Policy Benefit, by Product Segment [Line Items]
Percentage of future policy benefits out of policy liabilities	84.00%
Percentage of unpaid policy claims out of policy liabilities	4.00%
Percentage of unearned premiums out of policy liabilities	5.00%
Percentage of other poliyholders' funds out of policy liabilities	7.00%
Percentage of advanced premiums to unearned premiums	69.00%	73.00%
Percentage of annuities to other policyholders' fund	97.00%	98.00%
Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average interest rates reflected in the consolidated statements of earnings for future policy benefits	3.30%	3.40%	3.50%
Aflac U.S.
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average interest rates reflected in the consolidated statements of earnings for future policy benefits	5.30%	5.40%	5.50%
Health insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior year claims and claims adjustment expense	$ (563)	$ (518)	$ (465)
Health insurance | Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior year claims and claims adjustment expense	$ (419)
Percentage of total prior year claims and claims adjustment expense	74.00%
Liability for unpaid claims and claims adjustment expense, foreign currency translation gain (loss)	$ 14
Prior year claims and claims adjustment expense excluding effect of foreign currency	$ (404)
Percentage of total prior year claims and claims adjustment expense excluding effect of foreign currency	72.00%