Fair Value Measures - Differences Between Aggregate Fair Value and Aggregate Remaining Contractual Principal Balance Outstanding - Fair Value Option (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	$ 501	$ 624
Fair Value	511	630
Fair Value Over / (Under) UPB	10	6
Non-accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	3	4
Fair Value	3	4
Fair Value Over / (Under) UPB	0	0
Accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	498	620
Fair Value	508	626
Fair Value Over / (Under) UPB	10	6
Loans held for sale
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	501	557
Fair Value	511	564
Fair Value Over / (Under) UPB	10	7
Loans held for sale | Non-accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	3	4
Fair Value	3	4
Fair Value Over / (Under) UPB	0	0
Loans held for sale | Accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	498	553
Fair Value	508	560
Fair Value Over / (Under) UPB	10	7
Loans held-for-investment
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	0	67
Fair Value	0	66
Fair Value Over / (Under) UPB	0	(1)
Loans held-for-investment | Non-accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	0	0
Fair Value	0	0
Fair Value Over / (Under) UPB	0	0
Loans held-for-investment | Accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	0	67
Fair Value	0	66
Fair Value Over / (Under) UPB	$ 0	$ (1)