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Subsequent Events - Narrative (Details) - USD ($) | Oct. 01, 2020 | Oct. 13, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Dec. 31, 2018
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Subsequent Event [Line Items] |  |  |  |  |  |  |  |
Principal |  |  | $ 2,143,000,000 |  | $ 1,493,000,000 |  |  |
AOCI, other effects |  |  | 1,233,000,000 |  | 863,000,000 |  |  |
Accumulated Net Investment Gain (Loss) Attributable to Parent |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |
AOCI, other effects |  |  | 1,212,000,000 | $ 1,030,000,000 | 862,000,000 | $ 920,000,000 | $ 812,000,000 | $ 83,000,000
Subsequent event |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |
Inforce annuity business ceded | $ 6,000,000,000 |  |  |  |  |  |  |
Inforce annuity business ceded, percent of total inforce annuity business | 15.00% |  |  |  |  |  |  |
Subsequent event | Minimum |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |
Expected life of ceded reserves | 7 years |  |  |  |  |  |  |
Subsequent event | Minimum | Accumulated Net Investment Gain (Loss) Attributable to Parent |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |
AOCI, other effects | $ 275,000,000 |  |  |  |  |  |  |
Subsequent event | Maximum |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |
Expected life of ceded reserves | 10 years |  |  |  |  |  |  |
Subsequent event | Maximum | Accumulated Net Investment Gain (Loss) Attributable to Parent |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |
AOCI, other effects | $ 300,000,000 |  |  |  |  |  |  |
AFG | Subordinated Debentures |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |
Principal |  |  | 825,000,000 |  | 475,000,000 |  |  |
AFG | Subordinated Debentures | 6% Subordinated Debentures due November 2055 |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |
Principal |  |  | $ 150,000,000 |  | $ 150,000,000 |  |  |
Interest rate on debt instruments |  |  | 6.00% |  |  |  |  |
AFG | Subordinated Debentures | 6% Subordinated Debentures due November 2055 | Subsequent event |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |
Principal |  | $ 150,000,000 |  |  |  |  |  |
Interest rate on debt instruments |  | 6.00% |  |  |  |  |  |

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- Definition Inforce annuity business that been ceded to other entities, stated as a percent of total inforce annuity business. + References No definition available. + Details
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- Definition Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(30)(a)(4)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e637-108580 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(23)(a)(3)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669686-108580 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (h)(2) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (g)(2)(ii) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e681-108580 + Details
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