XML 79 R66.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Income Taxes - Narrative (Details) - USD ($) $ in Millions |  | 3 Months Ended
--- | --- | ---
Jan. 01, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Mar. 31, 2017
Income Tax Reconciliation [Line Items] |  |  |  |
Statutory rate of income taxes |  | 21.00% |  | 35.00%
Operating loss carryforwards subject to SRLY tax rules will expire unutilized at December 31, 2018 |  | $ 19 |  |
Tax Cuts and Jobs Act of 2017 |  |  |  |
Income Tax Reconciliation [Line Items] |  |  |  |
Statutory rate of income taxes | 21.00% |  |  |
Decrease in net deferred tax asset resulting from the changes in the Tax Cuts and Jobs Act of 2017 |  |  | $ 83 |

X
- Definition Amount of reported income tax expense (benefit) in excess of (less than) expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operations, attributable to Tax Cuts and Jobs Act. + References No definition available. + Details
Name: | afg_EffectiveIncomeTaxRateReconciliationTaxCutsandJobsActAmount
Namespace Prefix: | afg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Income Tax Reconciliation. + References No definition available. + Details
Name: | afg_IncomeTaxReconciliationLineItems
Namespace Prefix: | afg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of domestic federal statutory tax rate applicable to pretax income (loss). + References Reference 1: 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=84230637&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817 Reference 3: 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=84230637&loc=d3e32698-109319 + Details
Name: | us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under 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 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319 + Details
Name: | us-gaap_OperatingLossCarryforwards
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_IncomeTaxAuthorityAxis=afg_TaxCutsandJobsActof2017Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |