Loan Sales and Servicing Activities - Summary of Cash Flows with Transferees (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Cash flows:
Sales proceeds	$ 17,897,693	$ 11,375,408	$ 39,084,441	$ 34,208,217
Servicing fees received	149,210	123,626	426,774	354,535
Net servicing advances (recoveries)	8,605	$ 4,147	(23,583)	$ (20,572)
Period end information:
Unpaid principal balance of loans outstanding	159,638,921		159,638,921		$ 145,224,596
30-89 days	7,828,087		7,828,087		6,222,864
90 days or more - Not in foreclosure	2,480,348		2,480,348		2,208,083
90 days or more - In foreclosure	1,199,933		1,199,933		720,894
90 days or more - Foreclosed	11,369		11,369		24,243
Bankruptcy	$ 1,339,983		$ 1,339,983		$ 970,329