Long-Term Debt - Schedule of long-term debt (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Summary of Carrying value of long-term debt
Principal	$ 1,498	$ 1,498
Discount and Issue Costs	(23)	(23)
Carrying Value	1,475	1,475
AFG
Summary of Carrying value of long-term debt
Carrying Value	1,475	1,475
Senior Notes \| AFG
Summary of Carrying value of long-term debt
Principal	823	823
Discount and Issue Costs	(5)	(5)
Carrying Value	818	818
Senior Notes \| 4.50% Senior Notes due June 2047 \| AFG
Summary of Carrying value of long-term debt
Principal	567	567
Discount and Issue Costs	(1)	(1)
Carrying Value	$ 566	$ 566
Interest rate on debt instruments	4.50%	4.50%	4.50%
Senior Notes \| 5.25% Senior Notes due April 2030 \| AFG
Summary of Carrying value of long-term debt
Principal	$ 253	$ 253
Discount and Issue Costs	(4)	(4)
Carrying Value	$ 249	$ 249
Interest rate on debt instruments	5.25%	5.25%	5.25%
Senior Notes \| Other \| AFG
Summary of Carrying value of long-term debt
Principal	$ 3	$ 3
Discount and Issue Costs	0	0
Carrying Value	3	3
Subordinated Debentures \| AFG
Summary of Carrying value of long-term debt
Principal	675	675
Discount and Issue Costs	(18)	(18)
Carrying Value	657	657
Subordinated Debentures \| 4.50% Subordinated Debentures due September 2060 \| AFG
Summary of Carrying value of long-term debt
Principal	200	200
Discount and Issue Costs	(5)	(5)
Carrying Value	$ 195	195
Interest rate on debt instruments	4.50%
Subordinated Debentures \| 5.125% Subordinated Debentures due December 2059 \| AFG
Summary of Carrying value of long-term debt
Principal	$ 200	200
Discount and Issue Costs	(5)	(5)
Carrying Value	$ 195	195
Interest rate on debt instruments	5.125%
Subordinated Debentures \| 5.625% Subordinated Debentures due June 2060 \| AFG
Summary of Carrying value of long-term debt
Principal	$ 150	150
Discount and Issue Costs	(4)	(4)
Carrying Value	$ 146	146
Interest rate on debt instruments	5.625%
Subordinated Debentures \| 5.875% Subordinated Debentures due March 2059 \| AFG
Summary of Carrying value of long-term debt
Principal	$ 125	125
Discount and Issue Costs	(4)	(4)
Carrying Value	$ 121	$ 121
Interest rate on debt instruments	5.875%

Summary of Carrying value of long-term debt.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

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