BUSINESS SEGMENT INFORMATION - Operations by Segment - Assets (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 158,157	$ 165,086
Aflac Japan
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	130,611	137,271
Aflac U.S.
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	22,278	22,864
Corporate and other
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 5,268	$ 4,951