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Fair Value Measurements - Narrative (Details) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2017 USD ($) stock | Sep. 30, 2016 USD ($) stock | Sep. 30, 2017 USD ($) stock professional | Sep. 30, 2016 USD ($) stock | Dec. 31, 2016 USD ($)
Fair Value Measurements (Textual) [Abstract] |  |  |  |  |
AFG's internal investment professionals | professional |  |  | 25 |  |
Level 3 assets as a percentage of total assets measured at fair value |  |  | 5.00% |  |
Percentage of level 3 assets that were priced using non-binding broker quotes |  |  | 76.00% |  |
Level 3 assets that were priced using non-binding broker quotes |  |  | $ 1,610 |  |
Life contingent annuities | $ 207 |  | $ 207 |  | $ 204
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 | $ 2,290 |  | $ 2,290 |  |
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% |  |
Common stocks |  |  |  |  |
Fair Value Measurements (Textual) [Abstract] |  |  |  |  |
Number of stocks transferred from Level 1 to Level 2 | stock |  | 1 |  | 1 |
Fair value of assets transferred from Level 1 to Level 2, during the third quarter |  | $ 1 |  |  |
Fair Value of assets transferred from Level 1 to Level 2, during the first nine months |  | 1 |  | $ 1 |
Perpetual preferred stocks |  |  |  |  |
Fair Value Measurements (Textual) [Abstract] |  |  |  |  |
Number of stocks transferred from Level 2 to Level 1 | stock | 1 |  | 3 | 6 |
Fair value of assets transferred from Level 2 to Level 1, during the third quarter | $ 1 |  |  |  |
Fair Value of assets transferred from Level 2 to Level 1, during the first nine months | $ 17 | 35 | $ 17 | $ 35 |
Number of stocks transferred from Level 1 to Level 2 | stock |  |  |  | 5 |
Fair Value of assets transferred from Level 1 to Level 2, during the first nine months |  | $ 12 |  | $ 12 |

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