Fair Value Measurements - Unobservable inputs used in determining fair value of embedded derivatives (Details) - Embedded derivatives	3 Months Ended
Mar. 31, 2017
Unobservable inputs used by management in determining fair value of embedded derivatives
Risk margin for uncertainty in cash flows	0.68%
Minimum
Unobservable inputs used by management in determining fair value of embedded derivatives
Adjustment for insurance subsidiary's credit risk	0.20%
Surrenders	3.00%
Partial surrenders	2.00%
Annuitizations	0.10%
Deaths	1.50%
Budgeted option costs	2.40%
Maximum
Unobservable inputs used by management in determining fair value of embedded derivatives
Adjustment for insurance subsidiary's credit risk	2.80%
Surrenders	21.00%
Partial surrenders	10.00%
Annuitizations	1.00%
Deaths	8.00%
Budgeted option costs	3.60%

Risk associated with risk of annuitizations, expressed as a percentage, used as an input to measure fair value.

No definition available.

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- Definition

Risk associated with risk of budgeted option costs, expressed as a percentage, used as an input to measure fair value.

+ References

No definition available.

+ Details

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- Definition

Risk associated with risk of deaths, expressed as a percentage, used as an input to measure fair value.

+ References

No definition available.

+ Details

Name:	afg_FairValueInputsDeaths
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Data Type:	num:percentItemType
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Period Type:	duration

- Definition

Risk associated with risk of partial surrenders, expressed as a percentage, used as an input to measure fair value.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Risk associated with risk margin for uncertainty in cash flows, expressed as a percentage, used as an input to measure fair value.

+ References

No definition available.

+ Details

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Namespace Prefix:	afg_
Data Type:	num:percentItemType
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Period Type:	duration

- Definition

Risk associated with risk of surrenders, expressed as a percentage, used as an input to measure fair value.

+ References

No definition available.

+ Details

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- Definition

Unobservable inputs used in determining fair value of embedded derivatives.

+ References

No definition available.

+ Details

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- Definition

Risk associated with risk of default, credit spread risk and downgrade risk, expressed as a percentage, used as an input to measure fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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Period Type:	duration

- Details

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