Mortgage Loans Held for Portfolio (Mortgage Loans Held for Portfolio) (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable, Unpaid Principal Balance	$ 15,452	$ 14,453
Financing Receivable, Excluding Accrued Interest, after Allowance for Credit Loss	15,518	14,540
Residential Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable, Unpaid Principal Balance	15,452	14,453
Loans and Leases Receivable, Unamortized Premiums	157	156
Loans and Leases Receivable, Unamortized Discounts	(73)	(54)
Loans and Leases Receivable, Hedging Basis Adjustment	(12)	(9)
Financing Receivable, Allowance for Credit Loss, Noncurrent	15,524	14,546
Financing Receivable, Excluding Accrued Interest, after Allowance for Credit Loss	15,518	14,540
Loans and Leases Receivable, Allowance	(6)	(6)
Single Family [Member] \| Fixed rate, long-term single family mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable, Unpaid Principal Balance	14,522	13,549
Single Family [Member] \| Fixed rate, medium-term single family mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable, Unpaid Principal Balance	$ 930	$ 904

Reflects the cumulative amount of hedging adjustments that are being amortized into income as an adjustment of yield.

No definition available.

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Namespace Prefix:	fhlbdm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Reflects the cumulative amount of discounts from the face amount of loans that are being amortized into income as an adjustment of yield.

+ References

No definition available.

+ Details

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Namespace Prefix:	fhlbdm_
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Balance Type:	credit
Period Type:	instant

- Definition

Reflects the cumulative amount of premiums over the face amount of loans that are being amortized into income as an adjustment to yield.

+ References

No definition available.

+ Details

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Namespace Prefix:	fhlbdm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 20
-Name Accounting Standards Codification
-Section 40
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481628/310-20-40-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-2

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amortized cost excluding accrued interest, after allowance for credit loss, of financing receivable. Excludes net investment in lease.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-3B

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-5

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, fee, and loan in process, of financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Details

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Namespace Prefix:
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- Details

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- Details

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- Details

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