BUSINESS SEGMENT AND FOREIGN INFORMATION - Operations by Segment - Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 165,086	$ 152,768
Aflac Japan
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	137,271	127,523
Aflac U.S.
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	22,864	20,945
Corporate and other
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 4,951	$ 4,300