Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 12, 2019	Jun. 30, 2018
Entity Registrant Name	Aflac Incorporated
Entity Central Index Key	0000004977
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Amendment Flag	false
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Trading Symbol	AFL
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 33,002,565,252
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		750,332,375