Loan Sales and Servicing Activities - Summary of Cash Flows with Transferees (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows:
Sales proceeds	$ 61,214,102	$ 44,557,560	$ 50,235,245
Servicing fees received	587,919	488,483	376,160
Net servicing advances	36,277	28,557	$ 52,353
Period end information:
Unpaid principal balance of loans outstanding	168,842,011	145,224,596
30-89 days	7,947,560	6,222,864
90 days or more - Not in foreclosure	3,237,563	2,208,083
90 days or more - In foreclosure	888,136	720,894
90 days or more - Foreclosed	15,387	24,243
Bankruptcy	$ 1,343,816	$ 970,329