Schedule II - Aflac Incorporated (Parent Only) - Summary of Notes Payable (Detail 2) ¥ in Millions, $ in Millions	Dec. 31, 2022 JPY (¥)	Oct. 31, 2022	Sep. 30, 2022	Dec. 31, 2021 JPY (¥)	Apr. 30, 2021 JPY (¥)	Mar. 31, 2021 USD ($)	Apr. 30, 2020 USD ($)	Mar. 31, 2020 JPY (¥)	Dec. 31, 2019 JPY (¥)	Dec. 31, 2018	Oct. 31, 2018 JPY (¥)	Oct. 31, 2018 USD ($)	Oct. 31, 2017 JPY (¥)	Mar. 31, 2017 USD ($)	Jan. 31, 2017 JPY (¥)	Dec. 31, 2016	Sep. 30, 2016 USD ($)	Nov. 30, 2014 USD ($)	Aug. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)
3.625% senior notes due November 2024
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.625%		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%										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%
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				¥ 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%					0.50%
Debt instrument, principal amount	¥ 12,600			¥ 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				¥ 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%					0.843%
Debt instrument, principal amount	¥ 9,300			¥ 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%
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%					0.934%
Debt instrument, principal amount	¥ 9,800			¥ 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%
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%					1.122%
Debt instrument, principal amount	¥ 6,300			¥ 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	¥ 20,000
Parent Company | 3.625% senior notes due November 2024
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.625%		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%		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%
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%
Debt instrument, principal amount	¥ 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%
Debt instrument, principal amount	¥ 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%
Debt instrument, principal amount	¥ 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%
Debt instrument, principal amount	¥ 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%
Debt instrument, principal amount	¥ 20,000			¥ 20,000