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Regulatory and Capital Adequacy - Additional Information (Details) $ in Millions	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 capital	$ 43,501	$ 40,736
Common equity Tier 1 capital, capital ratio	0.131	0.137
Regulatory Capital Adjustments, Net of Tax, CECL Transition	$ 2,400
Common Equity Tier One Capital Ratio, CECL Transition	13.10%
Common Equity Tier One Capital Ratio, Excluding CECL Transition Adjustment	12.40%
Capital One Bank (USA), N.A.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Funds available for dividend payments	$ 531
Common equity Tier 1 capital	$ 17,392	$ 19,924
Common equity Tier 1 capital, capital ratio	0.165	0.215
Capital One, N.A.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Funds available for dividend payments	$ 447
Common equity Tier 1 capital	$ 26,699	$ 26,671
Common equity Tier 1 capital, capital ratio	0.111	0.124

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Common Equity Tier One Capital Ratio, CECL Transition

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Common Equity Tier One Capital Ratio, Excluding CECL Transition Adjustment

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Common equity Tier 1 capital ratio is a regulatory capital measure under Basel III calculated based on common equity Tier 1 capital divided by risk-weighted assets.

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Regulatory Capital Adjustments, Net of Tax, CECL Transition

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Amount of Common Equity Tier 1 risk-based capital as defined by regulatory framework.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826

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Amount of dividends available for payment after computation of statutory restrictions on capital surplus.

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