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Commitments, Guarantees and Contingent Liabilities - Guaranty funds and Guarantees (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Guaranty Funds |  |
Loss Contingencies |  |
Liability for insurance assessments | $ 12,000,000 | $ 13,000,000
Insurance assessments, premium tax offsets | 14,000,000 | $ 15,000,000
Minimum |  |
Loss Contingencies |  |
Reasonably possible additional losses | 0 |
Maximum |  |
Loss Contingencies |  |
Reasonably possible additional losses | $ 85,000,000 |

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- Definition The amount of insurance-related assessment liability that is expected to be recovered through a premium tax offset based on current laws applied to in-force policies. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 405 -SubTopic 30 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392405&loc=d3e24119-109301 + Details
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- Definition The liability as of the balance sheet date representing required funding mandated by statute or regulatory authority that is related directly or indirectly to underwriting activities, including pools for self-insurance and excluding premium taxes and income taxes. The funds derived from the assessments generally enable a government guarantor to pay insurance claims in the event that the underwriting insurer is insolvent or otherwise unable to meet its payment obligations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 405 -SubTopic 30 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392405&loc=d3e24119-109301 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 405 -SubTopic 30 -Section 15 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=99384745&loc=d3e23169-109297 + Details
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