XML 82 R41.htm IDEA: XBRL DOCUMENT v2.4.1.9
Fair Value Measurements (Details 2) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
US Treasury and Government [Member]    
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]    
Financial assets, Beginning Balance $ 15us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
$ 15us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
Impact of accounting change 0afg_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetImpactofAccountingChange
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Total realized/unrealized gains (losses) included in Net income 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
Total realized/unrealized gains (losses) included in other comprehensive income (loss) 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
Purchases and issuances 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
Sales and settlements 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
Transfer into Level 3 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
Transfer out of Level 3 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
Financial assets, Ending Balance 15us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
15us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
States, municipalities and political subdivisions [Member]    
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]    
Financial assets, Beginning Balance 100us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
61us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Impact of accounting change 0afg_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetImpactofAccountingChange
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Total realized/unrealized gains (losses) included in Net income 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Total realized/unrealized gains (losses) included in other comprehensive income (loss) 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Purchases and issuances 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Sales and settlements 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Transfer into Level 3 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Transfer out of Level 3 (39)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Financial assets, Ending Balance 61us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
61us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Residential Mortgage Backed Securities [Member]    
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]    
Financial assets, Beginning Balance 300us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
316us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Impact of accounting change 0afg_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetImpactofAccountingChange
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Total realized/unrealized gains (losses) included in Net income (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
1us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Total realized/unrealized gains (losses) included in other comprehensive income (loss) 3us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
4us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Purchases and issuances 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Sales and settlements (7)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
(8)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Transfer into Level 3 41us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
32us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Transfer out of Level 3 (30)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
(73)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Financial assets, Ending Balance 306us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
272us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Commercial Mortgage Backed Securities [Member]    
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]    
Financial assets, Beginning Balance 44us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
28us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Impact of accounting change 0afg_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetImpactofAccountingChange
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
 
Total realized/unrealized gains (losses) included in Net income 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Total realized/unrealized gains (losses) included in other comprehensive income (loss) 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Purchases and issuances 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Sales and settlements 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Transfer into Level 3 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Transfer out of Level 3 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Financial assets, Ending Balance 44us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
28us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Asset-backed Securities [Member]    
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]    
Financial assets, Beginning Balance 226us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
75us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
Impact of accounting change 0afg_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetImpactofAccountingChange
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
 
Total realized/unrealized gains (losses) included in Net income 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
Total realized/unrealized gains (losses) included in other comprehensive income (loss) 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
1us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
Purchases and issuances 5us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
50us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
Sales and settlements (41)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
(1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
Transfer into Level 3 21us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
81us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
Transfer out of Level 3 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
Financial assets, Ending Balance 211us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
206us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
All other corporate [Member]    
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]    
Financial assets, Beginning Balance 546us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
335us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
Impact of accounting change 0afg_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetImpactofAccountingChange
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
 
Total realized/unrealized gains (losses) included in Net income 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
1us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
Total realized/unrealized gains (losses) included in other comprehensive income (loss) 6us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
3us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
Purchases and issuances 44us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
1us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
Sales and settlements (13)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
(16)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
Transfer into Level 3 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
Transfer out of Level 3 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
(2)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
Financial assets, Ending Balance 583us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
322us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
Equity securities [Member]    
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]    
Financial assets, Beginning Balance 93us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
31us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
Impact of accounting change 0afg_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetImpactofAccountingChange
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
 
Total realized/unrealized gains (losses) included in Net income 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
1us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
Total realized/unrealized gains (losses) included in other comprehensive income (loss) (2)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
2us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
Purchases and issuances 10us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
30us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
Sales and settlements 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
(9)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
Transfer into Level 3 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
Transfer out of Level 3 (17)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
(14)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
Financial assets, Ending Balance 84us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
41us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquitySecuritiesMember
Assets of Managed Investment Entities [Member]    
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]    
Financial assets, Beginning Balance 31us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
30us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
Impact of accounting change 0afg_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetImpactofAccountingChange
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
 
Total realized/unrealized gains (losses) included in Net income (2)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
(1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
Total realized/unrealized gains (losses) included in other comprehensive income (loss) 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
Purchases and issuances 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
Sales and settlements 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
Transfer into Level 3 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
Transfer out of Level 3 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
Financial assets, Ending Balance $ 29us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember
$ 29us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= afg_AssetsOfManagedInvestmentEntitiesMember