STATUTORY ACCOUNTING AND DIVIDEND RESTRICTIONS - Profits Repatriated by Aflac Japan to Aflac U.S. (Detail) $ in Millions, ¥ in Billions	12 Months Ended
Dec. 31, 2017 USD ($)	Dec. 31, 2017 JPY (¥)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 JPY (¥)	Dec. 31, 2015 USD ($)	Dec. 31, 2015 JPY (¥)
Insurance [Abstract]
Profit repatriation	$ 1,150	¥ 129.3	$ 1,286	¥ 138.5	$ 2,139	¥ 259.0

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