Fair Value Measures - Differences Between Aggregate Fair Value and Aggregate Remaining Contractual Principal Balance Outstanding - Fair Value Option (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	$ 311	$ 624
Fair Value	317	630
Fair Value Over / (Under) UPB	6	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	307	620
Fair Value	313	626
Fair Value Over / (Under) UPB	6	6
Loans held for sale:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	311	557
Fair Value	317	564
Fair Value Over / (Under) UPB	6	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	307	553
Fair Value	313	560
Fair Value Over / (Under) UPB	6	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)