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Fair Value Measurements - Narrative (Details) $ in Millions | 3 Months Ended | 9 Months Ended |
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Sep. 30, 2016 USD ($) stock | Sep. 30, 2015 USD ($) stock | Mar. 31, 2015 USD ($) | Sep. 30, 2016 USD ($) stock professional | Sep. 30, 2015 USD ($) stock | Dec. 31, 2015 USD ($)
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 |  |  |  | 4.00% |  |
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 |  |  |  | $ 1,310 |  |
Life contingent annuities | $ 204 |  |  | $ 204 |  | $ 200
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 |  |  |  | 5.00% |  |
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 | $ 1,690 |  |  | $ 1,690 |  |
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 |  |  |  | 21.00% |  |
Common stocks |  |  |  |  |  |
Fair Value Measurements (Textual) [Abstract] |  |  |  |  |  |
Number of stocks transferred from Level 2 to Level 1 | stock |  | 1 |  |  | 7 |
Fair value of assets transferred from Level 2 to Level 1, during the first nine months |  | $ 80 |  |  | $ 80 |
Number of stocks transferred from Level 1 to Level 2 | stock | 1 |  |  | 1 |  |
Common stocks | Maximum |  |  |  |  |  |
Fair Value Measurements (Textual) [Abstract] |  |  |  |  |  |
Fair value of assets transferred from Level 2 to Level 1, during the third quarter |  | 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 |  |  |  | 6 | 4 |
Fair value of assets transferred from Level 2 to Level 1, during the first nine months | 35 | $ 19 |  | $ 35 | $ 19 |
Number of stocks transferred from Level 1 to Level 2 | stock |  | 7 |  | 5 | 7 |
Fair value of assets transferred from Level 1 to Level 2, during the third quarter |  | $ 31 |  |  |  |
Fair value of assets transferred from Level 1 to Level 2, during the first nine months | $ 12 | 31 |  | $ 12 | $ 31 |
Mandatorily redeemable preferred stocks |  |  |  |  |  |
Fair Value Measurements (Textual) [Abstract] |  |  |  |  |  |
Number of stocks transferred from Level 2 to Level 1 | stock |  |  |  |  | 1 |
Fair value of assets transferred from Level 2 to Level 1, during the first nine months |  | $ 10 |  |  | $ 10 |
Run-off long-term care insurance business |  |  |  |  |  |
Fair Value Measurements (Textual) [Abstract] |  |  |  |  |  |
Estimated sale proceeds of the run-off long-term care insurance business |  |  | $ 14 |  |  |

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