Schedule II - Aflac Incorporated (Parent Only) - Supplemental Disclosure of Cash Flow Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Shareholder dividend reinvestment
Condensed Cash Flow Statements, Captions [Line Items]
Treasury stock issued for shareholder dividend reinvestment	$ 30	$ 8	$ 29
Parent Company
Condensed Cash Flow Statements, Captions [Line Items]
Interest paid	189	179	195
Parent Company \| Shareholder dividend reinvestment
Condensed Cash Flow Statements, Captions [Line Items]
Treasury stock issued for shareholder dividend reinvestment	$ 30	$ 8	$ 29

The fair value of stock issued in noncash financing activities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586

Name:	us-gaap_StockIssued1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration