v3.25.3

Regulatory Capital Requirements (Summary Of Capital And Total Risk-Based Capital Ratios) (Details) $ in Thousands	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)
Capitol Federal Savings Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 leverage, Actual Amount	$ 935,267	$ 874,067
Tier 1 leverage, Actual Ratio	0.096	0.092
Tier 1 leverage, For Capital Adequacy Purposes, Amount	$ 876,469	$ 853,970
Tier 1 leverage, For Capital Adequacy Purposes, Ratio	0.090	0.090
Capitol Federal Financial Inc [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 leverage, Actual Amount	$ 984,902	$ 957,481
Tier 1 leverage, Actual Ratio	0.101	0.101
Tier 1 leverage, For Capital Adequacy Purposes, Amount	$ 876,448	$ 853,927
Tier 1 leverage, For Capital Adequacy Purposes, Ratio	0.090	0.090

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 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477270/942-505-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477270/942-505-50-1

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Amount of Tier 1 leverage capital as defined by regulatory framework.

+ References

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- Definition

Amount of minimum Tier 1 leverage capital required for capital adequacy as defined by regulatory framework.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477270/942-505-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477270/942-505-50-1B

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Ratio of minimum Tier 1 leverage capital to average assets required for capital adequacy as defined by regulatory framework.

+ References

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Ratio of Tier 1 capital to average assets as defined by regulatory framework.

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Capitol Federal Financial, Inc. 10-K