Mortgage Servicing Rights and Related Liabilities - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Servicing Asset at Amortized Cost [Line Items]
Excess spread financing - fair value	$ 815	$ 768
Mortgage servicing rights financing - fair value	30	$ 10
Forward MSRs Sold
Servicing Asset at Amortized Cost [Line Items]
UPB	361		$ 50
Forward MSRs Sold, Subservicing Retained
Servicing Asset at Amortized Cost [Line Items]
UPB	$ 342		$ 0