BUSINESS SEGMENT INFORMATION - Operations by Segment - Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 136,083	$ 129,819
Aflac Japan
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	113,625	107,858
Aflac U.S.
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	20,348	19,453
Other business segments
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	513	270
Total Business Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	134,486	127,581
Corporate and eliminations
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 1,597	$ 2,238