Income Taxes.

Name:	afg_IncomeTaxesTextualsAbstract
Namespace Prefix:	afg
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Income Tax Reconciliation.

+ Details

Name:	afg_IncomeTaxReconciliationLineItems
Namespace Prefix:	afg
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The sum of the differences between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to nondeductible expenses under enacted tax laws, or differences in the methodologies used to determine expense amounts for financial statements prepared in accordance with generally accepted accounting principles and enacted tax laws.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319

+ Details

Name:	us-gaap_IncomeTaxReconciliationNondeductibleExpense
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The portion of the difference between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to income that is exempt from income taxes under enacted tax laws.

+ References

+ Details

Name:	us-gaap_IncomeTaxReconciliationTaxExemptIncome
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The net amount of all increases and decreases in unrecognized tax benefits for the period.

+ References

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

-Publisher FASB

-Name FASB Interpretation (FIN)

-Number 48

-Paragraph 21

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 740

-SubTopic 10

-Section 50

-Paragraph 15A

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

+ Details

Name:	us-gaap_UnrecognizedTaxBenefitsPeriodIncreaseDecrease
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

Income Taxes (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
Income Taxes (Details) (USD $) In Millions	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Income Taxes (Textuals) [Abstract]
Change in AFG's liability for uncertain tax positions			$ 0
Variable Interest Entity, Primary Beneficiary [Member]
Income Tax Reconciliation [Line Items]
Non-deductible losses related to managed investment entities		4	47	37
Tax exempt income related to managed investment entities	$ 8