Schedule II - Aflac Incorporated (Parent Only) - Additional Information (Detail) $ in Millions, ¥ in Billions	Mar. 31, 2024 JPY (¥) series	Sep. 30, 2022 JPY (¥) series	Apr. 30, 2021 JPY (¥) series	Mar. 31, 2020 JPY (¥) series	Dec. 31, 2019 JPY (¥) series	Oct. 31, 2018 JPY (¥) series	Sep. 30, 2016 USD ($) series
Condensed Financial Statements, Captions [Line Items]
Number of Senior Notes Issued Through a Private Placement (in series)	5
Number of series of senior notes issued through a U.S. public debt offering (in series)	3	4	5	4	4	3	2
Private Placement
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Face Amount | ¥	¥ 75.0
Senior notes
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Face Amount	¥ 48.6	¥ 73.0	¥ 82.0	¥ 57.0	¥ 38.0	¥ 53.4	$ 700
Parent Company
Condensed Financial Statements, Captions [Line Items]
Number of Senior Notes Issued Through a Private Placement (in series)	5
Number of series of senior notes issued through a U.S. public debt offering (in series)	3
Parent Company | Private Placement
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Face Amount | ¥	¥ 75.0
Parent Company | Senior notes
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Face Amount | ¥	¥ 48.6