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Summary of Significant Accounting Policies - Recent Acquisitions (Details) (USD $)
Nov. 01, 2013
Feb. 17, 2012
May 01, 2012
account
Beech Street Capital      
Business Acquisition [Line Items]      
Value of acquired mortgage servicing portfolio $ 10,000,000,000cof_BusinessCombinationValueofAcquiredMortgageServicingPortfolio
/ us-gaap_BusinessAcquisitionAxis
= cof_BeechStreetCapitalMember		    
ING Direct Acquisition      
Business Acquisition [Line Items]      
Business combination, addition of loans   40,400,000,000cof_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedLoansReceivable
/ us-gaap_BusinessAcquisitionAxis
= cof_IngDirectMember		  
Business combination, other assets   53,900,000,000cof_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedNetOtherAssets
/ us-gaap_BusinessAcquisitionAxis
= cof_IngDirectMember		  
Business combination, deposits   84,400,000,000cof_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedDeposits
/ us-gaap_BusinessAcquisitionAxis
= cof_IngDirectMember		  
2012 U.S. Card Acquisition      
Business Acquisition [Line Items]      
Number of active accounts acquired     27,000,000cof_BusinessCombinationNumberofActiveAccountsAcquired
/ us-gaap_BusinessAcquisitionAxis
= cof_TwoThousandAndTwelveUnitedStatesCreditCardBusinessMember
Business combination, addition of loans     27,800,000,000cof_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedLoansReceivable
/ us-gaap_BusinessAcquisitionAxis
= cof_TwoThousandAndTwelveUnitedStatesCreditCardBusinessMember
Business combination, other assets     $ 327,000,000cof_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedNetOtherAssets
/ us-gaap_BusinessAcquisitionAxis
= cof_TwoThousandAndTwelveUnitedStatesCreditCardBusinessMember