Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Aflac Japan
Significant Accounting Policies [Line Items]
Aflac Japan's percentage of the Company's total revenues	74.00%	70.00%
Percentage of the Company Assets	84.00%		83.00%
Lower Limit
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Estimate, Effect of Adoption on Income Tax Expense (Benefit)	$ (2)
Upper Limit
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Estimate, Effect of Adoption on Income Tax Expense (Benefit)	$ (11)
Accounting Standards Update 2015-03
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Assets			$ (40)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Liabilities			$ (40)