BUSINESS SEGMENT AND FOREIGN INFORMATION - Operations by Segment - Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 137,217	$ 129,819	$ 118,256
Aflac Japan
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	114,402	107,858	97,646
Aflac U.S.
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	19,893	19,453	18,537
Other business segments
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	547	270	188
Total Business Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	134,842	127,581	116,371
Corporate and eliminations
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 2,375	$ 2,238	$ 1,885