XML 56 R41.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Accounting Policies - Narrative (Details) - USD ($) $ in Millions |  | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Jan. 01, 2018
Significant Accounting Policies [Line Items] |  |  |  |  |
Cumulative effect of accounting change | $ 4 |  | $ 4 |  |
Stranded amount reclassified from AOCI to retained earnings |  |  | $ 0 |  |
Weighted average common shares adjustment related to stock-based compensation |  | 1,600,000 | 2,000,000 | 1,600,000 |
Anti-dilutive potential common shares related to stock-based compensation plans |  | 0 | 0 | 400,000 |
Maturities of short term investments |  | 3 months |  |  |
Accounting Standards Update 2016-02 | Maximum |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Cumulative effect of accounting change |  | 0.50% |  |  |
Equity securities |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Available-for-sale securities, Equity securities | 1,600 |  | $ 1,600 |  |
Equity securities, trading at fair value | 62 |  | $ 62 |  |
Equity securities | Accounting Standards Update 2016-01 |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Cumulative effect of accounting change |  |  |  |  | $ (221)
Tax Cuts and Jobs Act of 2017 | Accounting Standards Update 2018-02 |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Stranded amount reclassified from AOCI to retained earnings | $ 145 |  |  |  |
Limited partnerships and similar investments | Accounting Standards Update 2016-01 |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Cumulative effect of accounting change |  |  |  |  | $ (4)
Equity securities still owned | Equity securities | Accounting Standards Update 2016-01 |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Net holding gains (losses) on equity securities |  | $ (257) |  |  |

X
- Definition Maturity period of short term investment maximum. + References No definition available. + Details
Name: | afg_MaturityPeriodOfShortTermInvestmentMaximum
Namespace Prefix: | afg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Net holding gains (losses) on equity securities in net earnings on securities that were still owned. All equity securities other than those accounted for under the equity method are carried at fair value through net earnings. + References No definition available. + Details
Name: | afg_NetHoldingGainsLossesOnEquitySecurities
Namespace Prefix: | afg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition New accounting pronouncement or change in accounting principle, effect of adoption, percent + References No definition available. + Details
Name: | afg_NewAccountingPronouncementorChangeinAccountingPrincipleEffectofAdoptionPercent
Namespace Prefix: | afg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect + References No definition available. + Details
Name: | afg_TaxCutsandJobsActReclassificationfromAOCItoRetainedEarningsTaxEffect
Namespace Prefix: | afg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
Name: | us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of equity securities categorized neither as held-to-maturity nor as trading. + References No definition available. + Details
Name: | us-gaap_AvailableForSaleSecuritiesEquitySecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption. + References No definition available. + Details
Name: | us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 28A -URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1500-109256 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
Name: | us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value of investments in trading equity securities and other forms of trading securities that provide ownership interests. + References No definition available. + Details
Name: | us-gaap_TradingSecuritiesEquity
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_VariableInterestEntityLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201602Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201601Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=afg_AccountingStandardsUpdate201802Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_LimitedPartnerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | afg_EquitySecuritiesAxis=afg_EquitySecuritiesStillOwnedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |