Schedule II - Aflac Incorporated (Parent Only) - Summary of Notes Payable and Lease Obligations (Detail 2) $ in Millions, ¥ in Billions	Dec. 31, 2025 JPY (¥)	Sep. 30, 2025	Jun. 30, 2025 JPY (¥)	May 31, 2025 JPY (¥)	Dec. 31, 2024 JPY (¥)	Mar. 31, 2024 JPY (¥)	Sep. 30, 2022 JPY (¥)	Aug. 31, 2022 JPY (¥)	Apr. 30, 2021 JPY (¥)	Mar. 31, 2021 USD ($)	Apr. 30, 2020 USD ($)	Mar. 31, 2020 JPY (¥)	Dec. 31, 2019 JPY (¥)	Oct. 31, 2018 JPY (¥)	Oct. 31, 2018 USD ($)	Oct. 31, 2017 JPY (¥)	Jan. 31, 2017 JPY (¥)	Dec. 31, 2016	Sep. 30, 2016 USD ($)	Aug. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)
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 notes 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 paid September 2025
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate		0.30%			0.30%							0.30%
Debt instrument, principal amount					¥ 12.4							¥ 12.4
.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	¥ 60.0				¥ 60.0												¥ 60.0
1.048% senior notes due March 2029
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.048%				1.048%	1.048%
Debt instrument, principal amount	¥ 13.0				¥ 13.0	¥ 13.0
1.075% senior notes due September 2029
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.075%				1.075%		1.075%
Debt instrument, principal amount	¥ 33.4				¥ 33.4		¥ 33.4
.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	¥ 12.6				¥ 12.6								¥ 12.6
.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	¥ 13.3				¥ 13.3							¥ 13.3
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	¥ 29.3				¥ 29.3									¥ 29.3
1.726% senior notes due October 2030
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.726%		1.726%
Debt instrument, principal amount	¥ 35.0		¥ 35.0
1.412% senior notes due March 2031
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.412%				1.412%	1.412%
Debt instrument, principal amount	¥ 27.9				¥ 27.9	¥ 27.9
.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	¥ 30.0				¥ 30.0				¥ 30.0
.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	¥ 9.3				¥ 9.3								¥ 9.3
.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	¥ 20.7				¥ 20.7							¥ 20.7
1.990% senior notes due May 2032
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.99%			1.99%
Debt instrument, principal amount	¥ 18.2			¥ 18.2
1.320% senior notes due December 2032
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.32%				1.32%		1.32%
Debt instrument, principal amount	¥ 21.1				¥ 21.1		¥ 21.1
2.003% senior notes due December 2032
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.003%		2.003%
Debt instrument, principal amount	¥ 23.4		¥ 23.4
.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	¥ 12.0				¥ 12.0				¥ 12.0
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	¥ 15.2				¥ 15.2									¥ 15.2
1.682% senior notes due March 2034
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.682%				1.682%	1.682%
Debt instrument, principal amount	¥ 7.7				¥ 7.7	¥ 7.7
1.600% senior notes due March 2034
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.60%				1.60%	1.60%
Debt instrument, principal amount	¥ 18.3				¥ 18.3	¥ 18.3
.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	¥ 9.8				¥ 9.8								¥ 9.8
.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	¥ 10.6				¥ 10.6							¥ 10.6
2.320% senior notes due May 2035
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.32%			2.32%
Debt instrument, principal amount	¥ 38.3			¥ 38.3
2.369% senior notes due June 2035
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.369%		2.369%
Debt instrument, principal amount	¥ 9.5		¥ 9.5
1.740% senior notes due March 2036
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.74%				1.74%	1.74%
Debt instrument, principal amount	¥ 15.0				¥ 15.0	¥ 15.0
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	¥ 10.0				¥ 10.0				¥ 10.0
1.594% senior notes due September 2037
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.594%				1.594%		1.594%
Debt instrument, principal amount	¥ 6.5				¥ 6.5		¥ 6.5
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	¥ 8.9				¥ 8.9									¥ 8.9
1.920% senior notes due March 2039
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.92%				1.92%	1.92%
Debt instrument, principal amount	¥ 16.5				¥ 16.5	¥ 16.5
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	¥ 6.3				¥ 6.3								¥ 6.3
2.650% senior notes due May 2040
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.65%			2.65%
Debt instrument, principal amount	¥ 11.6			¥ 11.6
2.779% senior notes due June 2040
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.779%		2.779%
Debt instrument, principal amount	¥ 7.0		¥ 7.0
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	¥ 10.0				¥ 10.0				¥ 10.0
2.160% senior notes due March 2044
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.16%				2.16%	2.16%
Debt instrument, principal amount	¥ 5.7				¥ 5.7	¥ 5.7
3.040% senior notes due May 2045
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.04%			3.04%
Debt instrument, principal amount	¥ 7.0			¥ 7.0
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	¥ 60.0				¥ 60.0											¥ 60.0
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	¥ 20.0				¥ 20.0				¥ 20.0
2.144% senior notes due September 2052
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.144%				2.144%		2.144%
Debt instrument, principal amount	¥ 12.0				¥ 12.0		¥ 12.0
2.400% senior notes due March 2054
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.40%				2.40%	2.40%
Debt instrument, principal amount	¥ 19.5				¥ 19.5	¥ 19.5
Yen-denominated loan variable interest rate due August 2027
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.08%				0.84%
Debt instrument, principal amount	¥ 11.7				¥ 11.7			¥ 11.7
Yen-denominated loan variable interest rate due August 2029
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.18%				0.94%
Debt instrument, principal amount	¥ 25.3				¥ 25.3			25.3
Yen-denominated loan variable interest rate due August 2032
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.33%				1.09%
Debt instrument, principal amount	¥ 70.0				¥ 70.0			¥ 70.0
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 notes 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 paid September 2025
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate		0.30%			0.30%
Debt instrument, principal amount					¥ 12.4
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	¥ 60.0				¥ 60.0
Parent Company | 1.048% senior notes due March 2029
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.048%				1.048%
Debt instrument, principal amount	¥ 13.0				¥ 13.0
Parent Company | 1.075% senior notes due September 2029
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.075%				1.075%
Debt instrument, principal amount	¥ 33.4				¥ 33.4
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	¥ 12.6				¥ 12.6
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	¥ 13.3				¥ 13.3
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	¥ 29.3				¥ 29.3
Parent Company | 1.726% senior notes due October 2030
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.726%		1.726%
Debt instrument, principal amount	¥ 35.0		¥ 35.0
Parent Company | 1.412% senior notes due March 2031
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.412%				1.412%
Debt instrument, principal amount	¥ 27.9				¥ 27.9
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	¥ 30.0				¥ 30.0
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	¥ 9.3				¥ 9.3
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	¥ 20.7				¥ 20.7
Parent Company | 1.990% senior notes due May 2032
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.99%			1.99%
Debt instrument, principal amount	¥ 18.2			¥ 18.2
Parent Company | 1.320% senior notes due December 2032
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.32%				1.32%
Debt instrument, principal amount	¥ 21.1				¥ 21.1
Parent Company | 2.003% senior notes due December 2032
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.003%		2.003%
Debt instrument, principal amount	¥ 23.4		¥ 23.4
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	¥ 12.0				¥ 12.0
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	¥ 15.2				¥ 15.2
Parent Company | 1.682% senior notes due March 2034
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.682%				1.682%
Debt instrument, principal amount	¥ 7.7				¥ 7.7
Parent Company | 1.600% senior notes due March 2034
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.60%				1.60%
Debt instrument, principal amount	¥ 18.3				¥ 18.3
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	¥ 9.8				¥ 9.8
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	¥ 10.6				¥ 10.6
Parent Company | 2.320% senior notes due May 2035
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.32%			2.32%
Debt instrument, principal amount	¥ 38.3			¥ 38.3
Parent Company | 2.369% senior notes due June 2035
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.369%		2.369%
Debt instrument, principal amount	¥ 9.5		¥ 9.5
Parent Company | 1.740% senior notes due March 2036
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.74%				1.74%
Debt instrument, principal amount	¥ 15.0				¥ 15.0
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	¥ 10.0				¥ 10.0
Parent Company | 1.594% senior notes due September 2037
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.594%				1.594%
Debt instrument, principal amount	¥ 6.5				¥ 6.5
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	¥ 8.9				¥ 8.9
Parent Company | 1.920% senior notes due March 2039
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.92%				1.92%
Debt instrument, principal amount	¥ 16.5				¥ 16.5
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	¥ 6.3				¥ 6.3
Parent Company | 2.650% senior notes due May 2040
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.65%			2.65%
Debt instrument, principal amount	¥ 11.6			¥ 11.6
Parent Company | 2.779% senior notes due June 2040
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.779%		2.779%
Debt instrument, principal amount	¥ 7.0		¥ 7.0
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	¥ 10.0				¥ 10.0
Parent Company | 2.160% senior notes due March 2044
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.16%				2.16%
Debt instrument, principal amount	¥ 5.7				¥ 5.7
Parent Company | 3.040% senior notes due May 2045
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.04%			3.04%
Debt instrument, principal amount	¥ 7.0			¥ 7.0
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	¥ 60.0				¥ 60.0
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	¥ 20.0				¥ 20.0
Parent Company | 2.144% senior notes due September 2052
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.144%				2.144%
Debt instrument, principal amount	¥ 12.0				¥ 12.0
Parent Company | 2.400% senior notes due March 2054
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.40%				2.40%
Debt instrument, principal amount	¥ 19.5				¥ 19.5
Parent Company | Yen-denominated loan variable interest rate due August 2027
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.08%				0.84%
Debt instrument, principal amount	¥ 11.7				¥ 11.7
Parent Company | Yen-denominated loan variable interest rate due August 2029
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.18%				0.94%
Debt instrument, principal amount	¥ 25.3				¥ 25.3
Parent Company | Yen-denominated loan variable interest rate due August 2032
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.33%				1.09%
Debt instrument, principal amount	¥ 70.0				¥ 70.0