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Fair Value Measurements - Narrative (Details) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2018 USD ($) professional | Mar. 31, 2017 USD ($) | Dec. 31, 2017 USD ($)
Fair Value Measurements (Textual) [Abstract] |  |  |
AFG's internal investment professionals | professional | 25 |  |
Fair Value of assets transferred from Level 1 to Level 2, during the first three months | $ 0 |  |
Fair Value of assets transferred from Level 2 to Level 1, during the first three months | $ 0 |  |
Level 3 assets as a percentage of total assets measured at fair value | 6.00% |  |
Percentage of level 3 assets that were priced using non-binding broker quotes | 78.00% |  |
Level 3 assets that were priced using non-binding broker quotes | $ 2,030 |  |
Fair value of equity securities transferred into Level 3 | 36 | $ 57 |
Life contingent annuities | $ 209 |  | $ 206
Maximum |  |  |
Fair Value Measurements (Textual) [Abstract] |  |  |
Percentage of internally developed Level 3 asset fair values to Shareholders' equity (are less than) | 10.00% |  |
Fixed-indexed annuties (embedded derivative), majority of future years | Minimum |  |  |
Fair Value Measurements (Textual) [Abstract] |  |  |
Unobservable input surrenders used in Level 3 fair value determination | 6.00% |  |
Fixed-indexed annuties (embedded derivative), majority of future years | Maximum |  |  |
Fair Value Measurements (Textual) [Abstract] |  |  |
Unobservable input surrenders used in Level 3 fair value determination | 10.00% |  |
Fixed-indexed annuities (embedded derivative) |  |  |
Fair Value Measurements (Textual) [Abstract] |  |  |
Fair value of derivatives in annuity benefits accumulated measured using a discounted cash flow approach | $ 2,550 |  |
Fixed-indexed annuities (embedded derivative) | Minimum |  |  |
Fair Value Measurements (Textual) [Abstract] |  |  |
Unobservable input surrenders used in Level 3 fair value determination | 3.00% |  |
Fixed-indexed annuities (embedded derivative) | Maximum |  |  |
Fair Value Measurements (Textual) [Abstract] |  |  |
Unobservable input surrenders used in Level 3 fair value determination | 23.00% |  |
Equity securities |  |  |
Fair Value Measurements (Textual) [Abstract] |  |  |
Fair value of equity securities transferred into Level 3 | $ 29 | $ 0 |

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- Definition Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226008-175313 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13495-108611 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 + Details
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