Asset-Backed Securities Issued - Components of Asset-Backed Securities Issued by Consolidated Securitization Entities Sponsored, Along With Other Selected Information (Details) - Asset-backed securities issued	Dec. 31, 2020 USD ($) series	Dec. 31, 2019 USD ($) series
Debt Instrument [Line Items]
Long-term debt	$ 7,100,661,000	$ 10,515,475,000
Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Long-term debt	257,778,000	197,110,000
Certificates with principal balance
Debt Instrument [Line Items]
Certificates	6,637,905,000	9,962,253,000
Interest-only certificates
Debt Instrument [Line Items]
Certificates	204,978,000	356,112,000
Legacy Sequoia
Debt Instrument [Line Items]
Long-term debt	$ 282,326,000	$ 402,465,000
Number of series | series	20	20
Legacy Sequoia | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Long-term debt	$ (47,805,000)	$ (18,873,000)
Legacy Sequoia | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	0.35%	1.94%
Legacy Sequoia | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	1.55%	3.26%
Legacy Sequoia | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 329,039,000	$ 420,056,000
Legacy Sequoia | Interest-only certificates
Debt Instrument [Line Items]
Certificates	1,092,000	1,282,000
Sequoia Choice
Debt Instrument [Line Items]
Long-term debt	$ 1,347,357,000	$ 2,037,198,000
Number of series | series	10	9
Sequoia Choice | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Long-term debt	$ 32,809,000	$ 40,965,000
Sequoia Choice | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	2.25%	4.40%
Sequoia Choice | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	5.04%	5.05%
Sequoia Choice | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 1,309,957,000	$ 1,979,719,000
Sequoia Choice | Interest-only certificates
Debt Instrument [Line Items]
Certificates	4,591,000	16,514,000
Freddie Mac SLST
Debt Instrument [Line Items]
Long-term debt	$ 1,993,919,000	$ 1,918,322,000
Range of weighted average interest rates, by series		3.50%
Number of series | series	3	2
Debt instrument, face amount	$ 205,000,000
Freddie Mac SLST | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Long-term debt	$ 104,439,000	$ 45,349,000
Freddie Mac SLST | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	3.50%
Freddie Mac SLST | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	4.75%
Freddie Mac SLST | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 1,866,145,000	1,842,682,000
Freddie Mac SLST | Interest-only certificates
Debt Instrument [Line Items]
Certificates	23,335,000	30,291,000
Freddie Mac K-Series
Debt Instrument [Line Items]
Long-term debt	$ 463,966,000	$ 4,156,239,000
Range of weighted average interest rates, by series	3.39%
Number of series | series	1	5
Freddie Mac K-Series | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Long-term debt	$ 34,601,000	$ 93,559,000
Freddie Mac K-Series | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series		3.35%
Freddie Mac K-Series | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series		4.35%
Freddie Mac K-Series | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	416,339,000	$ 3,844,789,000
Freddie Mac K-Series | Interest-only certificates
Debt Instrument [Line Items]
Certificates	13,026,000	217,891,000
CAFL
Debt Instrument [Line Items]
Long-term debt	$ 3,013,093,000	$ 2,001,251,000
Number of series | series	14	10
CAFL | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Long-term debt	$ 133,734,000	$ 36,110,000
CAFL | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	2.68%	3.25%
CAFL | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	5.42%	5.36%
CAFL | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 2,716,425,000	$ 1,875,007,000
CAFL | Interest-only certificates
Debt Instrument [Line Items]
Certificates	$ 162,934,000	$ 90,134,000