Line of Credit, Term

No definition available.

Name:	afg_LineOfCreditTerm
Namespace Prefix:	afg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

No definition available.

+ Details

Name:	afg_LongTermDebtMaturitiesRepaymentsOfPrincipalInCalendarYearFive
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

Name:	afg_LongTermDebtMaturitiesRepaymentsOfPrincipalInCalendarYearFour
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

Name:	afg_LongTermDebtMaturitiesRepaymentsOfPrincipalInCalendarYearOne
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

Name:	afg_LongTermDebtMaturitiesRepaymentsOfPrincipalInCalendarYearThree
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

Name:	afg_LongTermDebtMaturitiesRepaymentsOfPrincipalInCalendarYearTwo
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

Name:	afg_LongTermDebtMaturitiesRepaymentsOfPrincipalInRemainingCurrentYearPeriod
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Interest rate stated in the contractual debt agreement.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Interpretation (FIN)

-Number 45

-Paragraph 13

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_GuaranteeObligationsCurrentCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityAmountOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateDescription
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow from a borrowing with the highest claim on the assets of the entity in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle, if longer).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 19

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 18

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfSeniorLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Long-Term Debt (Details Textual) (USD $) In Millions, unless otherwise specified	9 Months Ended		9 Months Ended					1 Months Ended						1 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Scenario, Forecast [Member]	Sep. 30, 2012 Minimum [Member]	Sep. 30, 2012 Maximum [Member]	Sep. 30, 2012 9-7/8% Senior Notes due June 2019 [Member]	Sep. 30, 2012 6-3/8% Senior Notes due June 2042 [Member]	Jun. 30, 2012 6-3/8% Senior Notes due June 2042 [Member] AFG [Member]	Sep. 30, 2012 5-3/4% Senior Notes due August 2042 [Member]	Sep. 30, 2012 7% Senior Notes due September 2050 [Member]	Sep. 30, 2012 7-1/8% Senior Debentures due February 2034 [Member]	Sep. 30, 2012 7-1/2% Senior Debentures due November 2033 [Member]	Sep. 30, 2012 7-1/4% Senior Debentures due January 2034 [Member]	Aug. 31, 2012 5-3/4% Senior Notes Due In August 2042 [Member] AFG [Member]
Debt Instrument [Line Items]
Interest rate on debt instruments						9.875%	6.375%		5.75%	7.00%	7.125%	7.50%	7.25%
Interest rate on revolving debt facility	2.00%			1.75%	3.00%
Proceeds from Issuance of Senior Long-term Debt								$ 230						$ 125
Secured Borrowings guaranteed by AFG	16	17
Scheduled principal payments on debt in 2012	25
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
Scheduled principal payments on debt in 2017	0
AFG's revolving credit line	500		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
Line of credit, term			4 years