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Regulatory and Capital Adequacy - Additional Information (Details) - USD ($) $ in Billions	Dec. 31, 2019	Dec. 31, 2018
Cash Reserves, Federal Reserve Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Cash Reserve Deposit Required and Made	$ 1.7	$ 1.9
Capital One Bank (USA), N.A.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments	3.3
Capital One, N.A.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments	$ 4.7

X

- Definition

Cash deposited in a special reserve account for the exclusive benefit of customers pursuant to SEC Regulations.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=116631393&loc=SL116631396-227033

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+ References

No definition available.

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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