Long-Term Debt (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Summary of Carrying value of long-term debt
Long-term debt	$ 1,024	$ 1,061
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	34	71
Notes payable secured by real estate due 2015 through 2016	22	59
National Interstate bank credit facility	12	12
Senior Notes [Member] \| 9-7/8% Senior Notes due June 2019 [Member] \| AFG [Member]
Summary of Carrying value of long-term debt
Senior Notes	350	350
Senior Notes [Member] \| 6-3/8% Senior Notes due June 2042 [Member] \| AFG [Member]
Summary of Carrying value of long-term debt
Senior Notes	230	230
Senior Notes [Member] \| 5-3/4% Senior Notes due August 2042 [Member] \| AFG [Member]
Summary of Carrying value of long-term debt
Senior Notes	125	125
Senior Notes [Member] \| 7% Senior Notes due September 2050 [Member] \| AFG [Member]
Summary of Carrying value of long-term debt
Senior Notes	132	132
Subordinated Debt [Member] \| 6-1/4% Subordinated Debentures due September 2054 [Member] \| AFG [Member]
Summary of Carrying value of long-term debt
Subordinated Debentures	$ 150	$ 150

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

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- Definition

Summary of Carrying value of long-term debt.

+ References

No definition available.

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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- Definition

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.

+ References

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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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- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

+ References

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