Long-Term Debt - Narrative (Details) - USD ($)	1 Months Ended		9 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Jun. 03, 2022
Long-term Debt, Fiscal Year Maturity [Abstract]
Scheduled principal payments on debt remainder of fiscal year			$ 0
Scheduled principal payments on debt in year one			0
Scheduled principal payments on debt in year two			0
Scheduled principal payments on debt in year three			0
Scheduled principal payments on debt in year four			0
Scheduled principal payments on debt in year five			0
Scheduled principal payments on debt thereafter			1,500,000,000
Reductions of long-term debt			21,000,000	$ 436,000,000
3.50% Senior Notes due August 2026 | Senior Notes
Long-term Debt, Fiscal Year Maturity [Abstract]
Loss on retirement of debt		$ (6,000,000)
AFG
Long-term Debt, Fiscal Year Maturity [Abstract]
Revolving credit facility term	5 years
Revolving credit line			450,000,000
Amount borrowed under revolving credit facility			$ 0		$ 0
AFG | 4.50% Senior Notes due June 2047 | Senior Notes
Long-term Debt, Fiscal Year Maturity [Abstract]
Face amount of debt repurchased	$ 15,000,000			$ 4,000,000
Interest rate on debt instruments	4.50%		4.50%	4.50%
Amount of debt repurchased	$ 13,000,000			$ 3,000,000
AFG | 5.25% Senior Notes due April 2030 | Senior Notes
Long-term Debt, Fiscal Year Maturity [Abstract]
Face amount of debt repurchased	$ 8,000,000			$ 5,000,000
Interest rate on debt instruments	5.25%		5.25%	5.25%
Amount of debt repurchased	$ 8,000,000			$ 5,000,000
AFG | 3.50% Senior Notes due August 2026 | Senior Notes
Long-term Debt, Fiscal Year Maturity [Abstract]
Face amount of debt repurchased		$ 49,000,000				$ 376,000,000
Interest rate on debt instruments		3.50%
Amount of debt repurchased		$ 51,000,000
Reductions of long-term debt		$ 382,000,000
SOFR | AFG
Long-term Debt, Fiscal Year Maturity [Abstract]
Interest rate on revolving debt facility			1.25%
SOFR | AFG | Minimum
Long-term Debt, Fiscal Year Maturity [Abstract]
Interest rate on revolving debt facility	1.00%
SOFR | AFG | Maximum
Long-term Debt, Fiscal Year Maturity [Abstract]
Interest rate on revolving debt facility	1.75%