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Borrowings - Outstanding Debt Obligations (Details) £ in Millions, $ in Millions, $ in Millions | Mar. 31, 2024 USD ($) | Mar. 31, 2024 EUR (€) | Mar. 31, 2024 CAD ($) | Mar. 31, 2024 GBP (£) | Mar. 31, 2024 AUD ($) | Dec. 31, 2023 USD ($) | Dec. 31, 2023 EUR (€) | Dec. 31, 2023 CAD ($) | Dec. 31, 2023 GBP (£) | Sep. 30, 2021 USD ($) | Jul. 23, 2021 USD ($) | Apr. 27, 2021 USD ($) | Mar. 16, 2021 USD ($) | Dec. 01, 2020 USD ($) | Oct. 23, 2020 USD ($)
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Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate Principal Committed | $ 6,600,000,000 |  |  |  |  | $ 6,600,000,000 |  |  |  |  |  |  |  |  |
Outstanding Principal | 5,298,027,000 |  |  |  |  | 4,937,883,000 |  |  |  |  |  |  |  |  |
Carrying Value | 5,274,114,000 |  |  |  |  | 4,911,930,000 |  |  |  |  |  |  |  |  |
Unamortized Debt Issuance Costs | 23,913,000 |  |  |  |  | 25,953,000 |  |  |  |  |  |  |  |  |
Unused portion | 1,301,974,000 |  |  |  |  | 1,662,117,000 |  |  |  |  |  |  |  |  |
Amount available | 1,301,974,000 |  |  |  |  | 1,662,037,000 |  |  |  |  |  |  |  |  |
Jackson Hole Funding Facility | Line of Credit | Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate Principal Committed | 500,000,000 | € 0 |  |  |  | 500,000,000 | € 0 |  |  |  |  |  |  |  |
Outstanding Principal | 387,949,000 |  |  |  |  | 233,019,000 |  |  |  |  |  |  |  |  |
Carrying Value | 387,949,000 |  |  |  |  | 233,019,000 |  |  |  |  |  |  |  |  |
Unused portion | 112,051,000 |  |  |  |  | 266,981,000 |  |  |  |  |  |  |  |  |
Amount available | 112,051,000 |  |  |  |  | 266,981,000 |  |  |  |  |  |  |  |  |
Breckenridge Funding Facility | Line of Credit | Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate Principal Committed | 1,025,000,000 |  |  |  |  | 1,025,000,000 |  |  |  |  |  |  |  |  |
Outstanding Principal | 824,350,000 |  |  |  |  | 741,700,000 |  |  |  |  |  |  |  |  |
Carrying Value | 824,350,000 |  |  |  |  | 741,700,000 |  |  |  |  |  |  |  |  |
Unused portion | 200,650,000 |  |  |  |  | 283,300,000 |  |  |  |  |  |  |  |  |
Amount available | 200,650,000 |  |  |  |  | 283,300,000 |  |  |  |  |  |  |  |  |
Big Sky Funding Facility | Line of Credit | Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate Principal Committed | 500,000,000 |  |  |  |  | 500,000,000 |  |  |  |  |  |  |  |  |
Outstanding Principal | 500,000,000 |  |  |  |  | 480,906,000 |  |  |  |  |  |  |  |  |
Carrying Value | 500,000,000 |  |  |  |  | 480,906,000 |  |  |  |  |  |  |  |  |
Unused portion | 0 |  |  |  |  | 19,094,000 |  |  |  |  |  |  |  |  |
Amount available | 0 |  |  |  |  | 19,094,000 |  |  |  |  |  |  |  |  |
Revolving Credit Facility | Line of Credit | Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate Principal Committed | 1,775,000,000 | € 101,100,000 | $ 1.0 | £ 113.2 | $ 1.0 | 1,775,000,000 | € 94,400,000 | $ 1.0 | £ 66.9 |  |  |  |  |  |
Outstanding Principal | 785,728,000 |  |  |  |  | 682,258,000 |  |  |  |  |  |  |  |  |
Carrying Value | 785,728,000 |  |  |  |  | 682,258,000 |  |  |  |  |  |  |  |  |
Unused portion | 989,273,000 |  |  |  |  | 1,092,742,000 |  |  |  |  |  |  |  |  |
Amount available | 989,273,000 |  |  |  |  | 1,092,662,000 |  |  |  |  |  |  |  |  |
3.625% Notes Due 2026 | Unsecured debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate Principal Committed | 800,000,000 |  |  |  |  | 800,000,000 |  |  |  |  |  |  |  | $ 300,000,000 | $ 500,000,000
Outstanding Principal | 800,000,000 |  |  |  |  | 800,000,000 |  |  |  |  |  |  |  |  |
Carrying Value | 796,789,000 |  |  |  |  | 796,343,000 |  |  |  |  |  |  |  |  |
Unamortized Debt Issuance Costs | 3,211,000 |  |  |  |  | 3,657,000 |  |  |  |  |  |  |  |  |
2.750% Notes Due 2026 | Unsecured debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate Principal Committed | 700,000,000 |  |  |  |  | 700,000,000 |  |  |  |  |  | $ 300,000,000 | $ 400,000,000 |  |
Outstanding Principal | 700,000,000 |  |  |  |  | 700,000,000 |  |  |  |  |  |  |  |  |
Carrying Value | 695,647,000 |  |  |  |  | 695,206,000 |  |  |  |  |  |  |  |  |
Unamortized Debt Issuance Costs | 4,353,000 |  |  |  |  | 4,794,000 |  |  |  |  |  |  |  |  |
2.125% Senior Notes Due 2027 | Unsecured debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate Principal Committed | 650,000,000 |  |  |  |  | 650,000,000 |  |  |  |  | $ 650,000,000 |  |  |  |
Outstanding Principal | 650,000,000 |  |  |  |  | 650,000,000 |  |  |  |  |  |  |  |  |
Carrying Value | 642,097,000 |  |  |  |  | 641,412,000 |  |  |  |  |  |  |  |  |
Unamortized Debt Issuance Costs | 7,903,000 |  |  |  |  | 8,588,000 |  |  |  |  |  |  |  |  |
2.850% Notes Due 2028 | Unsecured debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate Principal Committed | 650,000,000 |  |  |  |  | 650,000,000 |  |  |  | $ 650,000,000 |  |  |  |  |
Outstanding Principal | 650,000,000 |  |  |  |  | 650,000,000 |  |  |  |  |  |  |  |  |
Carrying Value | 641,554,000 |  |  |  |  | 641,086,000 |  |  |  |  |  |  |  |  |
Unamortized Debt Issuance Costs | $ 8,446,000 |  |  |  |  | $ 8,914,000 |  |  |  |  |  |  |  |  |

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