Fair Value Measures - Differences Between Aggregate Fair Value and Aggregate Remaining Contractual Principal Balance Outstanding - Fair Value Option (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	$ 1,496	$ 871
Fair Value	1,519	896
Fair Value Over / (Under) UPB	23	25
Non-accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	16	2
Fair Value	16	2
Fair Value Over / (Under) UPB	0	0
Total other performing loans
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	1,480	869
Fair Value	1,503	894
Fair Value Over / (Under) UPB	23	25
Loans held for sale
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	1,426	871
Fair Value	1,451	896
Fair Value Over / (Under) UPB	25	25
Loans held for sale | Non-accrual loans:
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	16	2
Fair Value	16	2
Fair Value Over / (Under) UPB	0	0
Loans held for sale | Total other performing loans
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	1,410	869
Fair Value	1,435	894
Fair Value Over / (Under) UPB	25	25
Loans held-for-investment
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	70	0
Fair Value	68	0
Fair Value Over / (Under) UPB	(2)	0
Loans held-for-investment | Total other performing loans
Fair Value, Option, Quantitative Disclosures
Unpaid Principal Balance	70	0
Fair Value	68	0
Fair Value Over / (Under) UPB	$ (2)	$ 0