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 $ in Thousands	Mar. 31, 2020 USD ($) series	Dec. 31, 2019 USD ($) series
Debt Instrument [Line Items]
Market valuation adjustments	$ (217,932)	$ 197,110
Total FHLBC Borrowings	6,461,864	10,515,475
Certificates with principal balance
Debt Instrument [Line Items]
Certificates	6,534,612	9,962,253
Interest-only certificates
Debt Instrument [Line Items]
Certificates	145,184	356,112
Legacy Sequoia
Debt Instrument [Line Items]
Market valuation adjustments	(87,507)	(18,873)
Total FHLBC Borrowings	$ 312,201	$ 402,465
Number of series | series	20	20
Legacy Sequoia | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	1.81%	1.94%
Legacy Sequoia | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	2.91%	3.26%
Legacy Sequoia | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 398,352	$ 420,056
Legacy Sequoia | Interest-only certificates
Debt Instrument [Line Items]
Certificates	1,356	1,282
Sequoia Choice
Debt Instrument [Line Items]
Market valuation adjustments	2,836	40,965
Total FHLBC Borrowings	$ 1,790,094	$ 2,037,198
Number of series | series	9	9
Sequoia Choice | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	4.37%	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	$ 1,776,396	$ 1,979,719
Sequoia Choice | Interest-only certificates
Debt Instrument [Line Items]
Certificates	10,862	16,514
Freddie Mac SLST
Debt Instrument [Line Items]
Market valuation adjustments	0	45,349
Total FHLBC Borrowings	$ 1,825,000	$ 1,918,322
Range of weighted average interest rates, by series	3.50%	3.50%
Number of series | series	2	2
Freddie Mac SLST | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 1,800,218	$ 1,842,682
Freddie Mac SLST | Interest-only certificates
Debt Instrument [Line Items]
Certificates	24,782	30,291
Freddie Mac K-Series
Debt Instrument [Line Items]
Market valuation adjustments	15,104	93,559
Total FHLBC Borrowings	$ 447,699	$ 4,156,239
Range of weighted average interest rates, by series	3.53%
Number of series | series	1	5
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	$ 418,212	$ 3,844,789
Freddie Mac K-Series | Interest-only certificates
Debt Instrument [Line Items]
Certificates	14,383	217,891
CAFL
Debt Instrument [Line Items]
Market valuation adjustments	(148,365)	36,110
Total FHLBC Borrowings	$ 2,086,870	$ 2,001,251
Number of series | series	11	10
CAFL | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	3.22%	3.25%
CAFL | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	5.22%	5.36%
CAFL | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 2,141,434	$ 1,875,007
CAFL | Interest-only certificates
Debt Instrument [Line Items]
Certificates	$ 93,801	$ 90,134