Amount of long-term debt maturing within the fifth full calendar year following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements and other securities redeemable at fixed or determinable prices and dates.

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Amount of long-term debt maturing within the fourth full calendar year following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements and other securities redeemable at fixed or determinable prices and dates.

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Amount of long-term debt maturing within the first full calendar year following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements and other securities redeemable at fixed or determinable prices and dates.

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Amount of long-term debt maturing within the third full calendar year following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements and other securities redeemable at fixed or determinable prices and dates.

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Amount of long-term debt maturing within the second full calendar year following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements and other securities redeemable at fixed or determinable prices and dates.

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Amount of long-term debt maturing within the remaining current year period, which may include maturities of long-term debt, sinking fund requirements and other securities redeemable at fixed or determinable prices and dates.

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Long-term debt.

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Interest rate stated in the contractual debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

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Amount borrowed under the credit facility as of the balance sheet date.

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Increase for additional borrowings on the credit facility during the period.

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Description of the interest rate for the amounts borrowed under the credit facility, including the terms and the method for determining the interest rate (for example, fixed or variable, LIBOR plus a percentage, increasing rate, timing of interest rate resets, remarketing provisions).

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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The cash outflow from the repayment of long-term borrowing where a lender is placed in a lien position behind debt having a higher priority of repayment (senior) in case of liquidation of the entity's assets or underlying collateral.

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Long-Term Debt (Details Textuals) (USD $) In Millions, unless otherwise specified	6 Months Ended	9 Months Ended								1 Months Ended
	Jun. 30, 2010	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2011 9-7/8% Senior Notes due June 2019 [Member]	Sep. 30, 2011 7% Senior Notes due September 2050 [Member]	Sep. 30, 2011 7-1/2% Senior Debentures due November 2033 [Member]	Sep. 30, 2011 7-1/4% Senior Debentures due January 2034 [Member]	Sep. 30, 2011 7-1/8% Senior Debentures due February 2034 [Member]	Sep. 30, 2011 10-7/8% Subordinated Notes due May 2011 [Member]	May 31, 2011 10-7/8% Subordinated Notes due May 2011 [Member] Subsidiaries [Member]
Debt Instrument [Line Items]
American Premier 10-7/8% Subordinated Notes due May 2011										$ 8
Interest rate on debt instruments				9.875%	7.00%	7.50%	7.25%	7.125%	10.875%
Long-Term Debt (Textuals) [Abstract]
Secured Borrowings guaranteed by AFG		17	18
Scheduled principal payments on debt in 2011		3
Scheduled principal payments on debt in 2012		34
Scheduled principal payments on debt in 2013		20
Scheduled principal payments on debt in 2014		2
Scheduled principal payments on debt in 2015		14
Scheduled principal payments on debt in 2016		45
AFG's revolving credit line		500
Interest rate range for revolving credit facility		1.75% to 3.00% (currently 2%) over LIBOR
Amount borrowed under AFG revolving credit facility		0
Amount borrowed under National Interstate bank credit facility	$ 30