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Investment Information - Limited partnership interests (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
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Schedule of Equity Method Investments [Line Items] |  |  |
Maximum Exposure to Loss |  | $ 2,918,177 | $ 2,232,609
Aggregate unfunded commitments |  | 2,600,000 | 2,100,000
Equity method investments |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |
Maximum Exposure to Loss | [1] | 2,741,293 | 2,047,889
Aggregate unfunded commitments |  | 2,300,000 | 1,800,000
Fair value option |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |
Maximum Exposure to Loss | [2] | 176,884 | 184,720
Aggregate unfunded commitments |  | $ 22,900 | $ 35,600
[1] | Aggregate unfunded commitments were $2.3 billion at September 30, 2021, compared to $1.8 billion at December 31, 2020.
[2] | Aggregate unfunded commitments were $22.9 million at September 30, 2021, compared to $35.6 million at December 31, 2020.

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