Long-Term Debt - Schedule of long-term debt (Details) - USD ($) $ in Millions	Jun. 30, 2022	Jun. 03, 2022	Dec. 31, 2021
Summary of Carrying value of long-term debt
Principal	$ 1,568		$ 1,993
Discount and Issue Costs	(26)		(29)
Carrying Value	1,542		1,964
Senior Notes \| AFG
Summary of Carrying value of long-term debt
Principal	893		1,318
Discount and Issue Costs	(7)		(10)
Carrying Value	$ 886		1,308
Senior Notes \| 4.50% Senior Notes due June 2047 \| AFG
Debt Instrument [Line Items]
Interest rate on debt instruments	4.50%
Summary of Carrying value of long-term debt
Principal	$ 590		590
Discount and Issue Costs	(2)		(2)
Carrying Value	$ 588		588
Senior Notes \| 3.50% Senior Notes due August 2026 \| AFG
Debt Instrument [Line Items]
Interest rate on debt instruments	3.50%	3.50%
Summary of Carrying value of long-term debt
Principal	$ 0		425
Discount and Issue Costs	0		(3)
Carrying Value	$ 0		422
Senior Notes \| 5.25% Senior Notes due April 2030 \| AFG
Debt Instrument [Line Items]
Interest rate on debt instruments	5.25%
Summary of Carrying value of long-term debt
Principal	$ 300		300
Discount and Issue Costs	(5)		(5)
Carrying Value	295		295
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	(19)		(19)
Carrying Value	$ 656		656
Subordinated Debentures \| 4.50% Subordinated Debentures due September 2060 \| AFG
Debt Instrument [Line Items]
Interest rate on debt instruments	4.50%
Summary of Carrying value of long-term debt
Principal	$ 200		200
Discount and Issue Costs	(5)		(5)
Carrying Value	$ 195		195
Subordinated Debentures \| 5.125% Subordinated Debentures due December 2059 \| AFG
Debt Instrument [Line Items]
Interest rate on debt instruments	5.125%
Summary of Carrying value of long-term debt
Principal	$ 200		200
Discount and Issue Costs	(6)		(6)
Carrying Value	$ 194		194
Subordinated Debentures \| 5.625% Subordinated Debentures due June 2060 \| AFG
Debt Instrument [Line Items]
Interest rate on debt instruments	5.625%
Summary of Carrying value of long-term debt
Principal	$ 150		150
Discount and Issue Costs	(4)		(4)
Carrying Value	$ 146		146
Subordinated Debentures \| 5.875% Subordinated Debentures due March 2059 \| AFG
Debt Instrument [Line Items]
Interest rate on debt instruments	5.875%
Summary of Carrying value of long-term debt
Principal	$ 125		125
Discount and Issue Costs	(4)		(4)
Carrying Value	$ 121		$ 121

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

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