Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Summary of Carrying value of long-term debt
Long-term debt	$ 950	$ 953
Notes payable secured by real estate due 2013 through 2016	62	62
Secured borrowings ($15 and $16 guaranteed by AFG)	16	19
AFG [Member]
Summary of Carrying value of long-term debt
Other long-term debt	3	3
Long-term debt	840	840
Subsidiaries [Member]
Summary of Carrying value of long-term debt
Long-term debt	90	93
Notes payable secured by real estate due 2013 through 2016	62	62
Secured borrowings ($15 and $16 guaranteed by AFG)	16	19
National Interstate bank credit facility	12	12
9-7/8% Senior Notes due June 2019 [Member] \| AFG [Member]
Summary of Carrying value of long-term debt
Senior Notes	350	350
6-3/8% Senior Notes due June 2042 [Member] \| AFG [Member]
Summary of Carrying value of long-term debt
Senior Notes	230	230
5-3/4% Senior Notes due August 2042 [Member] \| AFG [Member]
Summary of Carrying value of long-term debt
Senior Notes	125	125
7% Senior Notes due September 2050 [Member] \| AFG [Member]
Summary of Carrying value of long-term debt
Senior Notes	132	132
Payable To Subsidiary Trusts [Member]
Summary of Carrying value of long-term debt
AAG Holding Variable Rate Subordinated Debentures due May 2033	$ 20	$ 20

Long term notes payable to banks that are secured by real estate assets.

No definition available.

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- Definition

Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer.

+ References

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Including the current and noncurrent portions, carrying value as of the balance sheet date of loans from a bank with maturities initially due after one year or beyond the normal operating cycle if longer.

+ References

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- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Including both current and noncurrent portions, carrying amount as of the balance sheet date of other forms of debt not elsewhere specified in the taxonomy with initial maturities beyond one year or beyond the normal operating cycle, if longer.

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- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

+ References

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