Schedule II - Aflac Incorporated (Parent Only) - Summary of Notes Payable and Lease Obligations (Detail 2) $ in Millions, ¥ in Billions	Dec. 31, 2024 JPY (¥)	Mar. 31, 2024 JPY (¥)	Dec. 31, 2023 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 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	¥ 12.4		¥ 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 2039
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.048%	1.048%
Debt instrument, principal amount	¥ 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
1.412% 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
.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
1.320% 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
.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%
Debt instrument, principal amount	¥ 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%
Debt instrument, principal amount	¥ 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
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
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%
Debt instrument, principal amount	¥ 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
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%
Debt instrument, principal amount	¥ 5.7	¥ 5.7
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%
Debt instrument, principal amount	¥ 19.5	¥ 19.5
Yen-denominated loan variable interest rate due August 2027
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.84%		0.35%
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	0.94%		0.45%
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	1.09%		0.60%
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 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	¥ 12.4		¥ 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 2039
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.048%	104.80%
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 | 1.412% 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 | 1.320% 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 | .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 | 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 | 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 | 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	0.84%		0.35%
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	0.94%		0.45%
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	1.09%		0.60%
Debt instrument, principal amount	¥ 70.0		¥ 70.0