Fair Value Measurements - Narrative (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2024 USD ($) loan investment	Dec. 31, 2023 USD ($) investment loan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment, at fair value	$ 11,283,775,000	$ 11,397,046,000
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment, at fair value	11,283,775,000	11,397,046,000
Investments with Difference Between Model Price and Third-Party Price | Securitized debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Excess of third party prices over (under) internally developed price, assets	$ (12,000,000)	$ (9,000,000)
Investments with Difference Between Model Price and Third-Party Price | Mortgage Backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans internally valued lower than third party prices | investment	7	1
Excess of third party prices over (under) internally developed price, assets	$ 1,000,000	$ 1,000,000
Investments with Difference Between Model Price and Third-Party Price | Securitized Loans Held For Investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Excess of third party prices over (under) internally developed price, assets	$ 3,000,000	$ 7,000,000
Internal Assessment | Investments with Difference Between Model Price and Third-Party Price | Securitized debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans internally valued lower than third party prices | investment	4	4
Assets, fair value disclosure	$ 224,000,000	$ 247,000,000
Internal Assessment | Investments with Difference Between Model Price and Third-Party Price | Mortgage Backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	$ 53,000,000	$ 6,000,000
Internal Assessment | Investments with Difference Between Model Price and Third-Party Price | Securitized Loans Held For Investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans internally valued lower than third party prices | loan	1	1
Assets, fair value disclosure	$ 55,000,000	$ 109,000,000
Third Party Assessment | Investments with Difference Between Model Price and Third-Party Price | Securitized debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Excess of third party prices over (under) internally developed price, assets	236,000,000	256,000,000
Third Party Assessment | Investments with Difference Between Model Price and Third-Party Price | Mortgage Backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	52,000,000	5,000,000
Third Party Assessment | Investments with Difference Between Model Price and Third-Party Price | Securitized Loans Held For Investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Excess of third party prices over (under) internally developed price, assets	$ 52,000,000	$ 102,000,000