Fair Value Measurements - Quantitative Information Used As Level 3 Inputs (Details) $ in Thousands	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	$ 2,494,954	$ 1,993,059
Other liabilities	(5,331)	(10,827)
Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	2,494,954	1,993,059
Other liabilities		(3,792)
Total other assets and (liabilities) measured at fair value on a recurring basis using Level 3 inputs	22,175,694	21,340,799
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	166,780	163,223
Other liabilities	(1,832)	(4,727)
Total other assets and (liabilities) measured at fair value on a recurring basis using Level 3 inputs	164,948	158,496
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Assumed and ceded (re)insurance contracts
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other liabilities	(1,832)	(4,727)
Fair Value, Measurements, Recurring | Internal valuation model | Significant Unobservable Inputs (Level 3) | Assumed and ceded (re)insurance contracts, group two
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other liabilities	(1,832)	(4,727)
Fair Value, Measurements, Recurring | Direct private equity investments | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	66,780	88,373
Fair Value, Measurements, Recurring | Direct private equity investments | Internal valuation model | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	66,780	88,373
Fair Value, Measurements, Recurring | Term loans | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	100,000	74,850
Fair Value, Measurements, Recurring | Term loans | Internal valuation model | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	100,000	74,900
Fair Value, Measurements, Recurring | Term loans | Discounted cash flow | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	$ 100,000	$ 74,850
Fair Value, Measurements, Recurring | Discount rate | Internal valuation model | Significant Unobservable Inputs (Level 3) | Assumed and ceded (re)insurance contracts, group two | Weighted Average or Actual
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant observable and unobservable inputs	0.040	0.013
Fair Value, Measurements, Recurring | Discount rate | Direct private equity investments | Internal valuation model | Significant Unobservable Inputs (Level 3) | Weighted Average or Actual
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant observable and unobservable inputs	0.075	0.075
Fair Value, Measurements, Recurring | Liquidity discount | Direct private equity investments | Internal valuation model | Significant Unobservable Inputs (Level 3) | Weighted Average or Actual
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant observable and unobservable inputs	0.150	0.150
Fair Value, Measurements, Recurring | Credit spread adjustment | Term loans | Discounted cash flow | Significant Unobservable Inputs (Level 3) | Weighted Average or Actual
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant observable and unobservable inputs	0.002	0.002
Fair Value, Measurements, Recurring | Risk premium | Term loans | Discounted cash flow | Significant Unobservable Inputs (Level 3) | Weighted Average or Actual
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant observable and unobservable inputs	0.026	0.026
Fair Value, Measurements, Recurring | Net undiscounted cash flows | Internal valuation model | Significant Unobservable Inputs (Level 3) | Assumed and ceded (re)insurance contracts, group two | Weighted Average or Actual
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant observable and unobservable inputs	14,734,000	14,920,000
Fair Value, Measurements, Recurring | Expected loss ratio | Internal valuation model | Significant Unobservable Inputs (Level 3) | Assumed and ceded (re)insurance contracts, group two | Weighted Average or Actual
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant observable and unobservable inputs	0.058	0.147