Consolidated Obligations (Systemwide Joint & Several Liability) (Details) - Guarantee of Indebtedness of Others [Member] - USD ($) $ in Millions	3 Months Ended
Jun. 30, 2025	Dec. 31, 2024
Obligation with Joint and Several Liability Arrangement [Line Items]
FHLB System total consolidated obligations	$ 1,232,127	$ 1,192,968
FHLB Chicago as primary obligor	$ 135,101	$ 120,091
Geographic Concentration Risk \| Total FHLB System Consolidated Obligations
Obligation with Joint and Several Liability Arrangement [Line Items]
As a percent of the FHLB System	11.00%	10.00%
Consolidated obligation bonds
Obligation with Joint and Several Liability Arrangement [Line Items]
FHLB System total consolidated obligations	$ 902,342	$ 863,788
FHLB Chicago as primary obligor	$ 71,055	$ 83,170
Consolidated obligation bonds \| Geographic Concentration Risk \| Total FHLB System Consolidated Obligations
Obligation with Joint and Several Liability Arrangement [Line Items]
As a percent of the FHLB System	8.00%	10.00%
Discount notes
Obligation with Joint and Several Liability Arrangement [Line Items]
FHLB System total consolidated obligations	$ 329,785	$ 329,180
FHLB Chicago as primary obligor	$ 64,046	$ 36,921
Discount notes \| Geographic Concentration Risk \| Total FHLB System Consolidated Obligations
Obligation with Joint and Several Liability Arrangement [Line Items]
As a percent of the FHLB System	19.00%	11.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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