BUSINESS SEGMENT AND FOREIGN INFORMATION - Information on Transfers of Funds from Aflac Japan (Detail) $ in Millions, ¥ in Billions	12 Months Ended
Dec. 31, 2020 USD ($)	Dec. 31, 2020 JPY (¥)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 JPY (¥)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 JPY (¥)
Segment Reporting [Abstract]
Management fees	$ 71		$ 75		$ 136
Allocated expenses	0		4		24
Profit remittances	1,215	¥ 129.8	2,070	¥ 225.2	808	¥ 89.7
Total transfers from Aflac Japan	$ 1,286		$ 2,149		$ 968

Amount of foreign earnings repatriated from subsidiaries outside the country of domicile.

No definition available.

Name:	us-gaap_ForeignEarningsRepatriated
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration