Fair Value Measurement - Differences Between Aggregate Fair Value and Aggregate Remaining Contractual Principal Balance Outstanding - Fair Value Option (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	$ 624	$ 871
Fair Value	630	896
Fair Value Over / (Under) UPB	6	25
Non-accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	4	2
Fair Value	4	2
Fair Value Over / (Under) UPB	0	0
Accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	620	869
Fair Value	626	894
Fair Value Over / (Under) UPB	6	25
Loans held for sale
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	557	871
Fair Value	564	896
Fair Value Over / (Under) UPB	7	25
Loans held for sale | Non-accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	4	2
Fair Value	4	2
Fair Value Over / (Under) UPB	0	0
Loans held for sale | Accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	553	869
Fair Value	560	894
Fair Value Over / (Under) UPB	7	25
Loans held-for-investment
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	67	0
Fair Value	66	0
Fair Value Over / (Under) UPB	(1)	0
Loans held-for-investment | Accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	67	0
Fair Value	66	0
Fair Value Over / (Under) UPB	$ (1)	$ 0