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Insurance - Narrative (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Carrying value of cash and securities owned by U.S.-based insurance subsidiaries on deposit |  | $ 1,040 |  |  |  |  |  |  |  |  | $ 1,040 |  |
Carrying value of cash and securities owned by insurance subsidiaries on deposit in support of underwriting activities at Lloyd's |  | 217 |  |  |  |  |  |  |  |  | 217 |  |
Undrawn letters of credit |  | 414 |  |  |  |  |  |  |  |  | 414 |  |
Undrawn letters of credit, collateralized |  | 0 |  |  |  |  |  |  |  |  | $ 0 |  |
Workers' compensation insurance discount rate |  |  |  |  |  |  |  |  |  |  | 4.50% | 4.50% |
Workers' compensation insurance discount, which has reduced the liability for unpaid losses and loss adjustment expenses |  | 12 |  |  |  | $ 13 |  |  |  |  | $ 12 | $ 13 |
Prior year claims and claims adjustment expense |  | 45 | $ 12 | $ 41 | $ 45 | 61 | $ 31 | $ 44 | $ 56 |  | 143 | 192 |
Long-term care insurance reserves, net of reinsurance recoverables |  | 46 |  |  |  | 45 |  |  |  |  | 46 | 45 |
Investment in Federal Home Loan Bank capital stock |  | 52 |  |  |  |  |  |  |  |  | 52 |  |
Advances from Federal Home Loan Bank |  | 1,100 |  |  |  | 1,100 |  |  |  |  | $ 1,100 | 1,100 |
Proceeds from Federal Home Loan Bank Advance, Investing Activities |  |  |  |  |  | 225 |  |  |  |  |  |  |
Description of variable rate basis |  |  |  |  |  |  |  |  |  |  | LIBOR |  |
Repayments of advances from Federal Home Loan Bank due in next twelve months |  | 310 |  |  |  |  |  |  |  |  | $ 310 |  |
Repayments of advances from Federal Home Loan Bank due in year two |  | 786 |  |  |  |  |  |  |  |  | 786 |  |
Fair value of fixed maturity investments held as collateral by the Federal Home Loan Bank |  | 1,270 |  |  |  |  |  |  |  |  | 1,270 |  |
Interest on advances from Federal Home Loan Bank |  |  |  |  |  |  |  |  |  |  | 27 | 20 | $ 14
Maximum amount of dividends available to be paid by insurance subsidiaries to AFG without prior approval of regulatory authorities |  | 852 |  |  |  |  |  |  |  |  | 852 |  |
Dividends on common stock |  |  |  |  |  |  |  |  |  |  | (446) | (397) | (421)
Aggregate guaranteed minimum death benefit value on variable annuity polices in force |  | 13 |  |  |  | 35 |  |  |  |  | 13 | 35 |
Minimum |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends payments without violating the most restrictive debt covenants, minimum |  | 2,500 |  |  |  |  |  |  |  |  | $ 2,500 |  |
Minimum | LIBOR |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
FHLB advances, basis spread on variable rate |  |  |  |  |  |  |  |  |  |  | 0.13% |  |
Maximum | LIBOR |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
FHLB advances, basis spread on variable rate |  |  |  |  |  |  |  |  |  |  | 0.21% |  |
Average | LIBOR |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
FHLB advances, basis spread on variable rate |  |  |  |  |  |  |  |  |  |  | 1.95% |  |
FHLB, advances, refinanced terms |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Advances from Federal Home Loan Bank |  | 610 |  |  |  | 40 |  |  |  |  | $ 610 | 40 |
Neon exited lines charge |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Prior year claims and claims adjustment expense |  |  |  |  |  |  |  |  |  |  | $ 7 | 0 | (18)
Catastrophe Bonds |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Catastrophe reinsurance coverage, excess retention percentage |  |  |  |  |  |  |  |  |  |  | 95.00% |  |
Catastrophe reinsurance coverage, excess retention amount |  |  |  |  |  |  |  |  |  |  | $ 200 |  |
Catastrophe reinsurance coverage, retention amount |  |  |  |  |  |  |  |  |  |  | 134 |  |
Catastrophe reinsurance coverage, annual cost |  |  |  |  |  |  |  |  |  |  | 11 |  |
Life insurance |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Increased statutory surplus resulting from reinsurance treaty |  | 2,868 |  |  |  | 2,701 |  |  |  |  | 2,868 | 2,701 |
Life insurance in force, ceded premiums |  | 6,230 |  |  |  | 7,690 |  |  |  |  | 6,230 | 7,690 |
Life insurance in force, direct premiums |  | $ 9,530 |  |  |  | 10,820 |  |  |  |  | 9,530 | 10,820 |
Reinsurance ceded |  |  |  |  |  |  |  |  |  |  | 20 | 22 | 28
Reinsurance recoveries |  |  |  |  |  |  |  |  |  |  | 32 | 38 | 35
Variable annuities | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Death benefits paid in excess of the variable annuity account balances |  |  |  |  |  |  |  |  |  |  | 1 | 1 | 1
Property and casualty insurance | Other lines |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Special A&E charges |  |  | $ 18 |  |  |  | $ 18 |  |  |  | $ 18 | 18 | 89
Neon Capital Limited | Property and casualty insurance |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Favorable reserve development related to certain lines of business within subsidiaries in connection with a reinsurance to close agreement |  |  |  |  |  |  |  |  |  | $ 42 |  |  |
Neon Capital Limited | Property and casualty insurance | Other lines |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Favorable reserve development related to certain lines of business within subsidiaries in connection with a reinsurance to close agreement |  |  |  |  |  |  |  |  |  | 18 |  |  | $ 18
Neon Capital Limited | Property and casualty insurance | Other lines | Reinsurance to close agreement |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Favorable reserve development related to certain lines of business within subsidiaries in connection with a reinsurance to close agreement | $ 18 |  |  |  |  |  |  |  |  |  |  |  |
Neon Capital Limited | Neon Capital Limited | Current lines |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Favorable reserve development related to certain lines of business within subsidiaries in connection with a reinsurance to close agreement |  |  |  |  |  |  |  |  |  | $ 24 |  |  |
Great American Life Insurance Company | Life insurance |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Increased statutory surplus resulting from reinsurance treaty |  |  |  |  |  | $ 510 |  |  |  |  |  | $ 510 |

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