Fair Value Disclosures - Assets Measured at Fair Value on a Non-Recurring Basis (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)
Assets, Fair Value Disclosure [Abstract]
Mortgage Loans held-for-investment, fair value	$ 7,107	$ 2,413
Fair Value, Measurements, Nonrecurring
Assets, Fair Value Disclosure [Abstract]
Mortgage Loans held-for-investment, fair value	1,230	1,777
Fair Value, Measurements, Nonrecurring \| Level 1
Assets, Fair Value Disclosure [Abstract]
Mortgage Loans held-for-investment, fair value	0	0
Fair Value, Measurements, Nonrecurring \| Level 2
Assets, Fair Value Disclosure [Abstract]
Mortgage Loans held-for-investment, fair value	241	303
Fair Value, Measurements, Nonrecurring \| Level 3
Assets, Fair Value Disclosure [Abstract]
Mortgage Loans held-for-investment, fair value	$ 989	$ 1,474
Fair Value, Measurements, Nonrecurring \| Level 3 \| Minimum \| Mortgage loans \| Median of external sources
Assets, Fair Value Disclosure [Abstract]
Fair Value Inputs External Pricing Sources	19.7	74.1
Fair Value, Measurements, Nonrecurring \| Level 3 \| Maximum \| Mortgage loans \| Median of external sources
Assets, Fair Value Disclosure [Abstract]
Fair Value Inputs External Pricing Sources	105.0	100.4
Fair Value, Measurements, Nonrecurring \| Level 3 \| Weighted Average \| Mortgage loans \| Median of external sources
Assets, Fair Value Disclosure [Abstract]
Fair Value Inputs External Pricing Sources	83.5	82.3