Loan Sales and Servicing Activities - Summary of Cash Flows with Transferees (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Cash flows:
Sales proceeds	$ 37,268,200	$ 19,337,017
Servicing fees received	195,782	$ 166,556
Period end information:
Unpaid principal balance of loans outstanding	211,289,054		$ 199,655,361
30-89 days	4,045,731		6,041,366
90 days or more - Not in foreclosure	15,506,434		17,799,621
90 days or more - In foreclosure	539,603		581,683
90 days or more - Foreclosed	9,207		10,893
Bankruptcy	1,204,192		1,230,696
30-89 days delinquent under CARES Act	1,695,953		2,626,617
90 days or more delinquent not in foreclosure under CARES Act	10,022,093		12,181,174
Total delinquent loans in COVID-19 pandemic related forbearance	$ 11,718,046		$ 14,807,791