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Investment Information - Limited partnership interests (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
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Schedule of Equity Method Investments [Line Items] |  |  |
On-Balance Sheet (Asset) Liability |  | $ 2,232,609 | $ 1,848,679
Aggregate commitments |  | 2,100,000 | 1,700,000
Equity method investments |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |
On-Balance Sheet (Asset) Liability | [1] | 2,047,889 | 1,660,396
Aggregate commitments |  | 1,800,000 | 1,400,000
Fair value option |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |
On-Balance Sheet (Asset) Liability | [2] | 184,720 | 188,283
Aggregate commitments |  | $ 35,600 | $ 41,700
[1] | Aggregate unfunded commitments were $1.8 billion at December 31, 2020, compared to $1.4 billion at December 31, 2019.
[2] | Aggregate unfunded commitments were $35.6 million at December 31, 2020, compared to $41.7 million at December 31, 2019.

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