Fair Value Measures - Differences Between Aggregate Fair Value and Aggregate Remaining Contractual Principal Balance Outstanding - Fair Value Option (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	$ 247	$ 624
Fair Value	249	630
Fair Value Over / (Under) UPB	2	6
Non-accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	4	4
Fair Value	4	4
Fair Value Over / (Under) UPB	0	0
Accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	243	620
Fair Value	245	626
Fair Value Over / (Under) UPB	2	6
Loans held for sale:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	247	557
Fair Value	249	564
Fair Value Over / (Under) UPB	2	7
Loans held for sale: | Non-accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	4	4
Fair Value	4	4
Fair Value Over / (Under) UPB	0	0
Loans held for sale: | Accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	243	553
Fair Value	245	560
Fair Value Over / (Under) UPB	2	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 | Accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	0	67
Fair Value	0	66
Fair Value Over / (Under) UPB	$ 0	$ (1)