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Long-Term Debt - Schedule of long-term debt (Details) - USD ($) $ in Millions | Mar. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Summary of Carrying value of long-term debt |  |
Principal | $ 1,993 | $ 1,993
Discount and Issue Costs | (30) | (30)
Carrying Value | 1,963 | 1,963
Senior Notes | AFG |  |
Summary of Carrying value of long-term debt |  |
Principal | 1,318 | 1,318
Discount and Issue Costs | (11) | (11)
Carrying Value | $ 1,307 | 1,307
Senior Notes | 4.50% Senior Notes due June 2047 | AFG |  |
Debt Instrument [Line Items] |  |
Interest rate on debt instruments | 4.50% |
Summary of Carrying value of long-term debt |  |
Principal | $ 590 | 590
Discount and Issue Costs | (2) | (2)
Carrying Value | $ 588 | 588
Senior Notes | 3.50% Senior Notes due August 2026 | AFG |  |
Debt Instrument [Line Items] |  |
Interest rate on debt instruments | 3.50% |
Summary of Carrying value of long-term debt |  |
Principal | $ 425 | 425
Discount and Issue Costs | (3) | (3)
Carrying Value | $ 422 | 422
Senior Notes | 5.25% Senior Notes due April 2030 | AFG |  |
Debt Instrument [Line Items] |  |
Interest rate on debt instruments | 5.25% |
Summary of Carrying value of long-term debt |  |
Principal | $ 300 | 300
Discount and Issue Costs | (6) | (6)
Carrying Value | 294 | 294
Senior Notes | Other | AFG |  |
Summary of Carrying value of long-term debt |  |
Principal | 3 | 3
Discount and Issue Costs | 0 | 0
Carrying Value | 3 | 3
Subordinated Debentures | AFG |  |
Summary of Carrying value of long-term debt |  |
Principal | 675 | 675
Discount and Issue Costs | (19) | (19)
Carrying Value | $ 656 | 656
Subordinated Debentures | 4.50% Subordinated Debentures due September 2060 | AFG |  |
Debt Instrument [Line Items] |  |
Interest rate on debt instruments | 4.50% |
Summary of Carrying value of long-term debt |  |
Principal | $ 200 | 200
Discount and Issue Costs | (5) | (5)
Carrying Value | $ 195 | 195
Subordinated Debentures | 5.125% Subordinate Debentures due December 2059 | AFG |  |
Debt Instrument [Line Items] |  |
Interest rate on debt instruments | 5.125% |
Summary of Carrying value of long-term debt |  |
Principal | $ 200 | 200
Discount and Issue Costs | (6) | (6)
Carrying Value | $ 194 | 194
Subordinated Debentures | 5.625% Subordinated Debentures due June 2060 | AFG |  |
Debt Instrument [Line Items] |  |
Interest rate on debt instruments | 5.625% |
Summary of Carrying value of long-term debt |  |
Principal | $ 150 | 150
Discount and Issue Costs | (4) | (4)
Carrying Value | $ 146 | 146
Subordinated Debentures | 5.875% Subordinated Debentures due March 2059 | AFG |  |
Debt Instrument [Line Items] |  |
Interest rate on debt instruments | 5.875% |
Summary of Carrying value of long-term debt |  |
Principal | $ 125 | 125
Discount and Issue Costs | (4) | (4)
Carrying Value | $ 121 | $ 121

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