Schedule II - Aflac Incorporated (Parent Only) - Summary of Notes Payable (Detail 2) ¥ in Millions, $ in Millions	Dec. 31, 2021 JPY (¥)	May 31, 2021	Apr. 30, 2021 JPY (¥)	Mar. 31, 2021 JPY (¥)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 JPY (¥)	Sep. 30, 2020 JPY (¥)	Apr. 30, 2020 USD ($)	Oct. 31, 2018 JPY (¥)	Oct. 31, 2018 USD ($)	Dec. 31, 2017	Oct. 31, 2017 JPY (¥)	Sep. 30, 2017 USD ($)	Jan. 31, 2017 JPY (¥)	Mar. 31, 2016 USD ($)	Nov. 30, 2014 USD ($)	Jun. 30, 2013 USD ($)	Aug. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)
3.625% senior notes paid May 2021
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.625%	3.625%				3.625%											3.625%
Debt instrument, principal amount | $																	$ 700
3.625% senior notes due November 2024
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.625%					3.625%										3.625%
Debt instrument, principal amount | $																$ 750
3.25% senior notes due March 2025
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.25%					3.25%									3.25%
Debt instrument, principal amount | $															$ 450
1.125% senior notes due March 2026
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.125%			1.125%	1.125%	1.125%
Debt instrument, principal amount | $					$ 400
2.875% senior notes due October 2026
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.875%					2.875%							2.875%
Debt instrument, principal amount | $													$ 300
3.60% senior notes due April 2030
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.60%					3.60%		3.60%
Debt instrument, principal amount | $								$ 1,000
6.90% senior notes due December 2039
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	6.90%					6.90%					6.90%
Debt instrument, principal amount | $																			$ 400
6.45% senior notes due August 2040
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	6.45%					6.45%					6.45%
Debt instrument, principal amount | $																		$ 450
4.00% senior noted due October 2046
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	4.00%					4.00%							4.00%
Debt instrument, principal amount | $													$ 400
4.750% senior notes due January 2049
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	4.75%					4.75%			4.75%	4.75%
Debt instrument, principal amount | $										$ 550
.300% senior notes due September 2025
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.30%			0.30%	0.30%
Debt instrument, principal amount	¥ 12,400			¥ 12,400
.932% senior notes due January 2027
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.932%					0.932%								0.932%
Debt instrument, principal amount	¥ 60,000					¥ 60,000								¥ 60,000
.500% senior notes due December 2029
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.50%					0.50%
Debt instrument, principal amount	¥ 12,600					¥ 12,600
.550% senior notes due March 2030
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.55%			0.55%	0.55%
Debt instrument, principal amount	¥ 13,300			¥ 13,300
1.159% senior notes due October 2030
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.159%					1.159%			1.159%	1.159%
Debt instrument, principal amount	¥ 29,300					¥ 29,300			¥ 29,300
.633% senior notes due April 2031
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.633%		0.633%			0.633%
Debt instrument, principal amount	¥ 30,000		¥ 30,000			¥ 30,000
.843% senior notes due December 2031
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.843%					0.843%
Debt instrument, principal amount	¥ 9,300					¥ 9,300
.750% senior notes due March 2032
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.75%			0.75%	0.75%	0.75%
Debt instrument, principal amount	¥ 20,700			¥ 20,700		¥ 20,700
.844% senior notes due April 2033
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.844%		0.844%			0.844%
Debt instrument, principal amount	¥ 12,000		¥ 12,000			¥ 12,000
1.488% senior notes due October 2033
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.488%					1.488%			1.488%	1.488%
Debt instrument, principal amount	¥ 15,200					¥ 15,200			¥ 15,200
.934% senior notes due December 2034
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.934%					0.934%
Debt instrument, principal amount	¥ 9,800					¥ 9,800
.830% senior notes due March 2035
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.83%			0.83%	0.83%	0.83%
Debt instrument, principal amount	¥ 10,600			¥ 10,600		¥ 10,600
1.039% senior notes due April 2036
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.039%		1.039%			1.039%
Debt instrument, principal amount	¥ 10,000		¥ 10,000			¥ 10,000
1.750% senior notes due October 2038
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.75%					1.75%			1.75%	1.75%
Debt instrument, principal amount	¥ 8,900					¥ 8,900			¥ 8,900
1.122% senior notes due December 2039
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.122%					1.122%
Debt instrument, principal amount	¥ 6,300					¥ 6,300
1.264% senior notes due April 2041
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.264%		1.264%			1.264%
Debt instrument, principal amount	¥ 10,000		¥ 10,000			¥ 10,000
2.108% subordinated notes due October 2047
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.108%					2.108%						2.108%
Debt instrument, principal amount	¥ 60,000					¥ 60,000						¥ 60,000
1.560% senior notes due April 2051
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.56%		1.56%			1.56%
Debt instrument, principal amount	¥ 20,000		¥ 20,000
Yen-denominated loan variable interest rate due September 2026
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.41%					0.43%
Debt instrument, principal amount	¥ 5,000					¥ 5,000	¥ 5,000
Yen-denominated loan variable interest rate due September 2029
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.56%					0.58%
Debt instrument, principal amount	¥ 25,000					¥ 25,000	¥ 25,000
Parent Company | 3.625% senior notes paid May 2021
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.625%	3.625%				3.625%
Parent Company | 3.625% senior notes due November 2024
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.625%					3.625%
Parent Company | 3.25% senior notes due March 2025
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.25%					3.25%
Parent Company | 1.125% senior notes due March 2026
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.125%			1.125%	1.125%	1.125%
Debt instrument, principal amount | $					$ 400
Parent Company | 2.875% senior notes due October 2026
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.875%					2.875%
Parent Company | 3.60% senior notes due April 2030
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.60%					3.60%
Parent Company | 6.90% senior notes due December 2039
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	6.90%					6.90%
Parent Company | 6.45% senior notes due August 2040
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	6.45%					6.45%
Parent Company | 4.00% senior noted due October 2046
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	4.00%					4.00%
Parent Company | 4.750% senior notes due January 2049
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	4.75%					4.75%
Parent Company | .300% senior notes due September 2025
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.30%					0.30%
Debt instrument, principal amount	¥ 12,400					¥ 12,400
Parent Company | .932% senior notes due January 2027
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.932%					0.932%
Debt instrument, principal amount	¥ 60,000					¥ 60,000
Parent Company | .500% senior notes due December 2029
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.50%					0.50%
Debt instrument, principal amount	¥ 12,600					¥ 12,600
Parent Company | .550% senior notes due March 2030
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.55%					0.55%
Debt instrument, principal amount	¥ 13,300					¥ 13,300
Parent Company | 1.159% senior notes due October 2030
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.159%					1.159%
Debt instrument, principal amount	¥ 29,300					¥ 29,300
Parent Company | .633% senior notes due April 2031
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.633%		0.633%			0.633%
Debt instrument, principal amount	¥ 30,000		¥ 30,000			¥ 30,000
Parent Company | .843% senior notes due December 2031
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.843%					0.843%
Debt instrument, principal amount	¥ 9,300					¥ 9,300
Parent Company | .750% senior notes due March 2032
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.75%					0.75%
Debt instrument, principal amount	¥ 20,700					¥ 20,700
Parent Company | .844% senior notes due April 2033
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.844%		0.844%			0.844%
Debt instrument, principal amount	¥ 12,000		¥ 12,000			¥ 12,000
Parent Company | 1.488% senior notes due October 2033
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.488%					1.488%
Debt instrument, principal amount	¥ 15,200					¥ 15,200
Parent Company | .934% senior notes due December 2034
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.934%					0.934%
Debt instrument, principal amount	¥ 9,800					¥ 9,800
Parent Company | .830% senior notes due March 2035
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.83%					0.83%
Debt instrument, principal amount	¥ 10,600					¥ 10,600
Parent Company | 1.039% senior notes due April 2036
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.039%		1.039%			1.039%
Debt instrument, principal amount	¥ 10,000		¥ 10,000			¥ 10,000
Parent Company | 1.750% senior notes due October 2038
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.75%					1.75%
Debt instrument, principal amount	¥ 8,900					¥ 8,900
Parent Company | 1.122% senior notes due December 2039
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.122%					1.122%
Debt instrument, principal amount	¥ 6,300					¥ 6,300
Parent Company | 1.264% senior notes due April 2041
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.264%		1.264%			1.264%
Debt instrument, principal amount	¥ 10,000		¥ 10,000			¥ 10,000
Parent Company | 2.108% subordinated notes due October 2047
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.108%					2.108%
Debt instrument, principal amount	¥ 60,000					¥ 60,000
Parent Company | 1.560% senior notes due April 2051
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.56%		1.56%			1.56%
Debt instrument, principal amount	¥ 20,000		¥ 20,000			¥ 20,000
Parent Company | Yen-denominated loan variable interest rate due September 2026
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.41%					0.43%
Debt instrument, principal amount	¥ 5,000					¥ 5,000
Parent Company | Yen-denominated loan variable interest rate due September 2029
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.56%					0.58%
Debt instrument, principal amount	¥ 25,000					¥ 25,000