INCOME TAXES (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Taxes [Line Items]
U.S. federal statutory corporate income tax rate	21.00%		35.00%	21.00%	35.00%	35.00%
Income Tax Expense, Gross, Continuing Operations, Adjustment of Deferred Tax Assets		$ 1,000
Income Tax Benefit, Gross, Continuing Operations, Adjustment of Deferred Tax Liabilities		2,900
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax Asset (Liability)		(1,900)
Deferred Tax Assets, Valuation Allowance		700				$ 700
Aflac Japan
Income Taxes [Line Items]
Deferred Tax Liabilities, Net		$ 4,500				$ 4,500