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FAIR VALUE MEASUREMENT - Valuation Techniques and Inputs for Level 3 Fair Value Measurements (Details) (Level 3, USD $)
0 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Mortgage-backed securities | Price-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets $ 2,388,000,000us-gaap_AssetsFairValueDisclosure
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$ 2,874,000,000us-gaap_AssetsFairValueDisclosure
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Mortgage-backed securities | Price-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 10.00c_FairValueInputsPrice
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0.00c_FairValueInputsPrice
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Mortgage-backed securities | Price-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 110.21c_FairValueInputsPrice
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127.87c_FairValueInputsPrice
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Mortgage-backed securities | Price-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 81.78c_FairValueInputsPrice
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81.43c_FairValueInputsPrice
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Mortgage-backed securities | Yield analysis
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets 1,138,000,000us-gaap_AssetsFairValueDisclosure
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= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
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1,117,000,000us-gaap_AssetsFairValueDisclosure
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Mortgage-backed securities | Yield analysis | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 0.67%c_FairValueInputsYield
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0.01%c_FairValueInputsYield
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Mortgage-backed securities | Yield analysis | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 29.53%c_FairValueInputsYield
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19.91%c_FairValueInputsYield
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Mortgage-backed securities | Yield analysis | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 4.45%c_FairValueInputsYield
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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5.89%c_FairValueInputsYield
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State and municipal, foreign government, corporate, and other debt securities | Cash flow
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets 1,530,000,000us-gaap_AssetsFairValueDisclosure
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= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
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1,860,000,000us-gaap_AssetsFairValueDisclosure
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= us-gaap_DebtSecuritiesMember
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= c_CashflowValuationTechniqueMember
State and municipal, foreign government, corporate, and other debt securities | Cash flow | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Credit spread (as a percent) 0.25%c_FairValueInputsCreditSpread
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0.25%c_FairValueInputsCreditSpread
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State and municipal, foreign government, corporate, and other debt securities | Cash flow | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Credit spread (as a percent) 6.00%c_FairValueInputsCreditSpread
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6.00%c_FairValueInputsCreditSpread
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State and municipal, foreign government, corporate, and other debt securities | Cash flow | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Credit spread (as a percent) 2.78%c_FairValueInputsCreditSpread
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2.33%c_FairValueInputsCreditSpread
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State and municipal, foreign government, corporate, and other debt securities | Price-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets 5,997,000,000us-gaap_AssetsFairValueDisclosure
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5,937,000,000us-gaap_AssetsFairValueDisclosure
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State and municipal, foreign government, corporate, and other debt securities | Price-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 0.00c_FairValueInputsPrice
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0.00c_FairValueInputsPrice
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State and municipal, foreign government, corporate, and other debt securities | Price-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 147.00c_FairValueInputsPrice
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124.00c_FairValueInputsPrice
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State and municipal, foreign government, corporate, and other debt securities | Price-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 87.65c_FairValueInputsPrice
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90.62c_FairValueInputsPrice
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Equity securities | Cash flow
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets 505,000,000us-gaap_AssetsFairValueDisclosure
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= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
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679,000,000us-gaap_AssetsFairValueDisclosure
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/ invest_InvestmentAxis
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/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
Equity securities | Cash flow | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 4.00%c_FairValueInputsYield
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4.00%c_FairValueInputsYield
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WAL (in years) 0 years 3 days 0 years 4 days
Equity securities | Cash flow | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 5.00%c_FairValueInputsYield
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5.00%c_FairValueInputsYield
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WAL (in years) 3 years 8 months 20 days 3 years 1 month 22 days
Equity securities | Cash flow | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 4.50%c_FairValueInputsYield
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4.50%c_FairValueInputsYield
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WAL (in years) 1 year 26 days 1 year 26 days
Equity securities | Price-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets 2,539,000,000us-gaap_AssetsFairValueDisclosure
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= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_EquitySecuritiesMember
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2,163,000,000us-gaap_AssetsFairValueDisclosure
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/ invest_InvestmentAxis
= us-gaap_EquitySecuritiesMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Equity securities | Price-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 0.00c_FairValueInputsPrice
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= us-gaap_EquitySecuritiesMember
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0.00c_FairValueInputsPrice
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Equity securities | Price-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 146.22c_FairValueInputsPrice
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141.00c_FairValueInputsPrice
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= c_PriceBasedValuationTechniqueMember
Equity securities | Price-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 91.88c_FairValueInputsPrice
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91.00c_FairValueInputsPrice
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Asset-backed securities | Price-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets 3,669,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
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3,607,000,000us-gaap_AssetsFairValueDisclosure
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= us-gaap_FairValueInputsLevel3Member
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= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ValuationTechniqueAxis
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Asset-backed securities | Price-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 4.25c_FairValueInputsPrice
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0.00c_FairValueInputsPrice
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Asset-backed securities | Price-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 100.35c_FairValueInputsPrice
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105.50c_FairValueInputsPrice
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Asset-backed securities | Price-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 71.18c_FairValueInputsPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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67.01c_FairValueInputsPrice
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= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
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= c_PriceBasedValuationTechniqueMember
Non-marketable equity securities | Price-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets 1,073,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
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1,224,000,000us-gaap_AssetsFairValueDisclosure
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/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Non-marketable equity securities | Price-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Discount to price (as a percent)   0.00%c_FairValueInputsDiscountToPrice
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EBITDA multiples 2.00us-gaap_FairValueInputsEarningsBeforeInterestTaxesDepreciationAndAmortizationMultiple
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Price-earnings ratio 8.10c_FairValueInputsPriceEarningsRatio
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Price-to-book ratio 1.04c_FairValueInputsPriceToBookRatio
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Fund NAV 1c_FairValueInputsFundNetAssetValue
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/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
 
Non-marketable equity securities | Price-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Discount to price (as a percent)   90.00%c_FairValueInputsDiscountToPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
EBITDA multiples 12.00us-gaap_FairValueInputsEarningsBeforeInterestTaxesDepreciationAndAmortizationMultiple
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
 
Price-earnings ratio 18.20c_FairValueInputsPriceEarningsRatio
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
 
Price-to-book ratio 2.03c_FairValueInputsPriceToBookRatio
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
 
Fund NAV 62,880,962c_FairValueInputsFundNetAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
 
Non-marketable equity securities | Price-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Discount to price (as a percent)   4.04%c_FairValueInputsDiscountToPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
EBITDA multiples 9.91us-gaap_FairValueInputsEarningsBeforeInterestTaxesDepreciationAndAmortizationMultiple
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
 
Price-earnings ratio 8.69c_FairValueInputsPriceEarningsRatio
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
 
Price-to-book ratio 1.24c_FairValueInputsPriceToBookRatio
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
 
Fund NAV 28,520,572c_FairValueInputsFundNetAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
 
Non-marketable equity securities | Comparables Analysis
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets 1,087,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
1,055,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
Non-marketable equity securities | Comparables Analysis | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Discount to price (as a percent) 0.00%c_FairValueInputsDiscountToPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
 
EBITDA multiples   2.90us-gaap_FairValueInputsEarningsBeforeInterestTaxesDepreciationAndAmortizationMultiple
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
Price-earnings ratio   8.10c_FairValueInputsPriceEarningsRatio
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
Price-to-book ratio   0.99c_FairValueInputsPriceToBookRatio
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
Fund NAV   1c_FairValueInputsFundNetAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
Non-marketable equity securities | Comparables Analysis | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Discount to price (as a percent) 100.00%c_FairValueInputsDiscountToPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
 
EBITDA multiples   13.10us-gaap_FairValueInputsEarningsBeforeInterestTaxesDepreciationAndAmortizationMultiple
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
Price-earnings ratio   13.10c_FairValueInputsPriceEarningsRatio
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
Price-to-book ratio   1.56c_FairValueInputsPriceToBookRatio
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
Fund NAV   64,668,171c_FairValueInputsFundNetAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
Non-marketable equity securities | Comparables Analysis | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Discount to price (as a percent) 7.51%c_FairValueInputsDiscountToPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
 
EBITDA multiples   9.77us-gaap_FairValueInputsEarningsBeforeInterestTaxesDepreciationAndAmortizationMultiple
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
Price-earnings ratio   8.43c_FairValueInputsPriceEarningsRatio
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
Price-to-book ratio   1.15c_FairValueInputsPriceToBookRatio
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
Fund NAV   29,975,777c_FairValueInputsFundNetAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= c_NonMarketableEquitySecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ComparablesAnalysisValuationTechniqueMember
Trading account assets and liabilities | Interest rate contracts | Model-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Fair value (gross) 7,674,000,000c_FairValueAssetLiabilityGross
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
8,309,000,000c_FairValueAssetLiabilityGross
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Interest rate contracts | Model-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
IR lognormal volatility (as a percent)   18.05%c_FairValueInputsInterestRateLognormalVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Mean reversion (as a percent) (7.94%)c_FairValueInputsMeanReversion
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
1.00%c_FairValueInputsMeanReversion
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Interest rate contracts | Model-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
IR lognormal volatility (as a percent)   90.65%c_FairValueInputsInterestRateLognormalVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Mean reversion (as a percent) 20.00%c_FairValueInputsMeanReversion
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
20.00%c_FairValueInputsMeanReversion
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Interest rate contracts | Model-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
IR lognormal volatility (as a percent)   30.21%c_FairValueInputsInterestRateLognormalVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Mean reversion (as a percent) 0.69%c_FairValueInputsMeanReversion
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
10.50%c_FairValueInputsMeanReversion
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Foreign exchange contracts | Model-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Fair value (gross) 1,952,000,000c_FairValueAssetLiabilityGross
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
1,428,000,000c_FairValueAssetLiabilityGross
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Foreign exchange contracts | Model-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Foreign exchange (FX) volatility (as a percent) 1.75%c_FairValueInputsForeignExchangeVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
0.37%c_FairValueInputsForeignExchangeVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Foreign exchange contracts | Model-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Foreign exchange (FX) volatility (as a percent) 32.34%c_FairValueInputsForeignExchangeVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
58.40%c_FairValueInputsForeignExchangeVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Foreign exchange contracts | Model-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Foreign exchange (FX) volatility (as a percent) 11.08%c_FairValueInputsForeignExchangeVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
8.57%c_FairValueInputsForeignExchangeVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Foreign exchange contracts | Cash flow
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Fair value (gross) 323,000,000c_FairValueAssetLiabilityGross
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
294,000,000c_FairValueAssetLiabilityGross
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
Trading account assets and liabilities | Foreign exchange contracts | Cash flow | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Interest rate (as a percent) 3.72%c_FairValueInputsInterestRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
3.72%c_FairValueInputsInterestRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
Contingent event probability (as a percent) 80.00%c_FairValueInputsContingentEventProbability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
 
Yield (as a percent) 0.22%c_FairValueInputsYield
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
 
IR-FX correlation (as a percent)   40.00%c_FairValueInputsInterestRateForeignExchangeCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
Trading account assets and liabilities | Foreign exchange contracts | Cash flow | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Interest rate (as a percent) 6.00%c_FairValueInputsInterestRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
8.27%c_FairValueInputsInterestRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
Contingent event probability (as a percent) 99.00%c_FairValueInputsContingentEventProbability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
 
Yield (as a percent) 12.30%c_FairValueInputsYield
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
 
IR-FX correlation (as a percent)   60.00%c_FairValueInputsInterestRateForeignExchangeCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
Trading account assets and liabilities | Foreign exchange contracts | Cash flow | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Interest rate (as a percent) 5.98%c_FairValueInputsInterestRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
5.02%c_FairValueInputsInterestRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
Contingent event probability (as a percent) 96.00%c_FairValueInputsContingentEventProbability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
 
Yield (as a percent) 3.39%c_FairValueInputsYield
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
 
IR-FX correlation (as a percent)   50.00%c_FairValueInputsInterestRateForeignExchangeCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
Trading account assets and liabilities | Equity contracts | Model-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Fair value (gross) 4,550,000,000c_FairValueAssetLiabilityGross
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
4,431,000,000c_FairValueAssetLiabilityGross
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Equity contracts | Model-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Equity volatility (as a percent) 10.00%c_FairValueInputsEquityVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
9.56%c_FairValueInputsEquityVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Equity-FX correlation (as a percent) (88.20%)c_FairValueInputsEquityForeignExchangeCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Equity-Equity correlation (as a percent) (66.30%)c_FairValueInputsEquityCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Forward price (as a percent) 90.70%c_FairValueInputsForwardPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Trading account assets and liabilities | Equity contracts | Model-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Equity volatility (as a percent) 76.62%c_FairValueInputsEquityVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
82.44%c_FairValueInputsEquityVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Equity-FX correlation (as a percent) 50.90%c_FairValueInputsEquityForeignExchangeCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Equity-Equity correlation (as a percent) 94.50%c_FairValueInputsEquityCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Forward price (as a percent) 111.88%c_FairValueInputsForwardPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Trading account assets and liabilities | Equity contracts | Model-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Equity volatility (as a percent) 25.89%c_FairValueInputsEquityVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
24.61%c_FairValueInputsEquityVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Equity-FX correlation (as a percent) (38.70%)c_FairValueInputsEquityForeignExchangeCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Equity-Equity correlation (as a percent) 34.80%c_FairValueInputsEquityCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Forward price (as a percent) 95.79%c_FairValueInputsForwardPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Trading account assets and liabilities | Equity contracts | Price-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Fair value (gross)   502,000,000c_FairValueAssetLiabilityGross
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Trading account assets and liabilities | Equity contracts | Price-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price   0.01c_FairValueInputsPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Equity forward (as a percent)   84.10%c_FairValueInputsEquityForward
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Equity-FX correlation (as a percent)   (88.20%)c_FairValueInputsEquityForeignExchangeCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Equity-Equity correlation (as a percent)   (66.30%)c_FairValueInputsEquityCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Trading account assets and liabilities | Equity contracts | Price-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price   144.50c_FairValueInputsPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Equity forward (as a percent)   100.80%c_FairValueInputsEquityForward
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Equity-FX correlation (as a percent)   48.70%c_FairValueInputsEquityForeignExchangeCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Equity-Equity correlation (as a percent)   94.80%c_FairValueInputsEquityCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Trading account assets and liabilities | Equity contracts | Price-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price   93.05c_FairValueInputsPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Equity forward (as a percent)   94.10%c_FairValueInputsEquityForward
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Equity-FX correlation (as a percent)   (25.17%)c_FairValueInputsEquityForeignExchangeCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Equity-Equity correlation (as a percent)   36.87%c_FairValueInputsEquityCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EquityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Trading account assets and liabilities | Commodity contracts | Model-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Fair value (gross) 3,576,000,000c_FairValueAssetLiabilityGross
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
3,606,000,000c_FairValueAssetLiabilityGross
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Commodity contracts | Model-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Commodity volatility (as a percent) 5.00%c_FairValueInputsCommodityVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
5.00%c_FairValueInputsCommodityVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Commodity correlation (as a percent) (52.00%)c_FairValueInputsCommodityCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
(57.00%)c_FairValueInputsCommodityCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Forward price (as a percent) 34.02%c_FairValueInputsForwardPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
35.34%c_FairValueInputsForwardPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Commodity contracts | Model-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Commodity volatility (as a percent) 60.00%c_FairValueInputsCommodityVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
83.00%c_FairValueInputsCommodityVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Commodity correlation (as a percent) 91.00%c_FairValueInputsCommodityCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
91.00%c_FairValueInputsCommodityCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Forward price (as a percent) 242.86%c_FairValueInputsForwardPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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/ us-gaap_FinancialInstrumentAxis
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/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
268.77%c_FairValueInputsForwardPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Commodity contracts | Model-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Commodity volatility (as a percent) 20.00%c_FairValueInputsCommodityVolatility
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
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/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
24.00%c_FairValueInputsCommodityVolatility
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= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
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/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Commodity correlation (as a percent) 38.00%c_FairValueInputsCommodityCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
30.00%c_FairValueInputsCommodityCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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/ us-gaap_FinancialInstrumentAxis
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/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Forward price (as a percent) 98.00%c_FairValueInputsForwardPrice
/ us-gaap_DerivativeInstrumentRiskAxis
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
101.74%c_FairValueInputsForwardPrice
/ us-gaap_DerivativeInstrumentRiskAxis
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
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/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Credit derivatives | Model-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Fair value (gross) 4,426,000,000c_FairValueAssetLiabilityGross
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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/ us-gaap_FinancialInstrumentAxis
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/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
4,944,000,000c_FairValueAssetLiabilityGross
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Credit derivatives | Model-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Recovery rate (as a percent) 18.31%c_FairValueInputsRecoveryRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
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/ us-gaap_RangeAxis
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/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
13.97%c_FairValueInputsRecoveryRate
/ us-gaap_DerivativeInstrumentRiskAxis
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
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/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Credit derivatives | Model-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Recovery rate (as a percent) 75.00%c_FairValueInputsRecoveryRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
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/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
75.00%c_FairValueInputsRecoveryRate
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
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/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Credit derivatives | Model-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Recovery rate (as a percent) 38.75%c_FairValueInputsRecoveryRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
37.62%c_FairValueInputsRecoveryRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Trading account assets and liabilities | Credit derivatives | Price-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Fair value (gross) 1,299,000,000c_FairValueAssetLiabilityGross
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
1,584,000,000c_FairValueAssetLiabilityGross
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= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Trading account assets and liabilities | Credit derivatives | Price-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 0.10c_FairValueInputsPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
1.00c_FairValueInputsPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Credit spread (as a percent) 0.04%c_FairValueInputsCreditSpread
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
0.01%c_FairValueInputsCreditSpread
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Credit correlation (as a percent) 5.00%c_FairValueInputsCreditCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
0.00%c_FairValueInputsCreditCorrelation
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Upfront points   0.39c_FairValueInputsUpfrontPoints
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
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/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Trading account assets and liabilities | Credit derivatives | Price-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 147.00c_FairValueInputsPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
144.50c_FairValueInputsPrice
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Credit spread (as a percent) 13.93%c_FairValueInputsCreditSpread
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
33.80%c_FairValueInputsCreditSpread
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Credit correlation (as a percent) 95.00%c_FairValueInputsCreditCorrelation
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= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
95.00%c_FairValueInputsCreditCorrelation
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Upfront points   100.00c_FairValueInputsUpfrontPoints
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= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Trading account assets and liabilities | Credit derivatives | Price-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 43.22c_FairValueInputsPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
53.86c_FairValueInputsPrice
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Credit spread (as a percent) 1.50%c_FairValueInputsCreditSpread
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
1.80%c_FairValueInputsCreditSpread
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Credit correlation (as a percent) 50.70%c_FairValueInputsCreditCorrelation
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= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
58.76%c_FairValueInputsCreditCorrelation
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= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Upfront points   52.26c_FairValueInputsUpfrontPoints
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= us-gaap_CreditRiskContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_TradingAccountAssetsAndTradingLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Nontrading derivatives and other financial assets and liabilities | Model-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Fair value (gross) 81,000,000c_FairValueAssetLiabilityGross
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
74,000,000c_FairValueAssetLiabilityGross
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Nontrading derivatives and other financial assets and liabilities | Model-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Redemption rate (as a percent) 13.00%c_FairValueInputsRedemptionRate
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
13.00%c_FairValueInputsRedemptionRate
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Nontrading derivatives and other financial assets and liabilities | Model-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Redemption rate (as a percent) 99.50%c_FairValueInputsRedemptionRate
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
99.50%c_FairValueInputsRedemptionRate
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Nontrading derivatives and other financial assets and liabilities | Model-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Redemption rate (as a percent) 67.20%c_FairValueInputsRedemptionRate
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
68.73%c_FairValueInputsRedemptionRate
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Nontrading derivatives and other financial assets and liabilities | Price-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Fair value (gross) 25,000,000c_FairValueAssetLiabilityGross
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
11,000,000c_FairValueAssetLiabilityGross
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Nontrading derivatives and other financial assets and liabilities | Price-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Fund NAV   12,974c_FairValueInputsFundNetAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Forward price (as a percent)   107.00%c_FairValueInputsForwardPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Nontrading derivatives and other financial assets and liabilities | Price-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Fund NAV   10,087,963c_FairValueInputsFundNetAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Forward price (as a percent)   107.10%c_FairValueInputsForwardPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Nontrading derivatives and other financial assets and liabilities | Price-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Fund NAV   9,308,012c_FairValueInputsFundNetAssetValue
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Forward price (as a percent)   107.05%c_FairValueInputsForwardPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Nontrading derivatives and other financial assets and liabilities | Yield analysis
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Fair value (gross) 47,000,000c_FairValueAssetLiabilityGross
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_ValuationTechniqueAxis
= c_YieldAnalysisValuationTechniqueMember
 
Nontrading derivatives and other financial assets and liabilities | Yield analysis | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 1.33%c_FairValueInputsYield
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
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= c_YieldAnalysisValuationTechniqueMember
 
Nontrading derivatives and other financial assets and liabilities | Yield analysis | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 5.78%c_FairValueInputsYield
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_YieldAnalysisValuationTechniqueMember
 
Nontrading derivatives and other financial assets and liabilities | Yield analysis | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 3.32%c_FairValueInputsYield
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= c_OtherFinancialAssetsAndLiabilitiesIncludingNonTradingDerivativesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_YieldAnalysisValuationTechniqueMember
 
Fixed income securities
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price for instrument valued at par 100c_FairValueInputsPriceforInstrumentValuedatPar
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FinancialInstrumentAxis
= us-gaap_FixedIncomeSecuritiesMember
 
Interest-bearing deposits | Model-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Liabilities 465,000,000us-gaap_LiabilitiesFairValueDisclosure
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
486,000,000us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Interest-bearing deposits | Model-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Commodity volatility (as a percent) 5.00%c_FairValueInputsCommodityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
5.00%c_FairValueInputsCommodityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Commodity correlation (as a percent) (52.00%)c_FairValueInputsCommodityCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
(57.00%)c_FairValueInputsCommodityCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Forward price (as a percent) 34.02%c_FairValueInputsForwardPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
35.34%c_FairValueInputsForwardPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Equity-IR correlation (as a percent) 34.00%c_FairValueInputsEquityInterestRateCorrelation
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
34.00%c_FairValueInputsEquityInterestRateCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Interest-bearing deposits | Model-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Commodity volatility (as a percent) 60.00%c_FairValueInputsCommodityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
83.00%c_FairValueInputsCommodityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Commodity correlation (as a percent) 91.00%c_FairValueInputsCommodityCorrelation
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
91.00%c_FairValueInputsCommodityCorrelation
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Forward price (as a percent) 242.86%c_FairValueInputsForwardPrice
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
268.77%c_FairValueInputsForwardPrice
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Equity-IR correlation (as a percent) 37.00%c_FairValueInputsEquityInterestRateCorrelation
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
37.00%c_FairValueInputsEquityInterestRateCorrelation
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Interest-bearing deposits | Model-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Commodity volatility (as a percent) 20.00%c_FairValueInputsCommodityVolatility
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
24.00%c_FairValueInputsCommodityVolatility
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Commodity correlation (as a percent) 38.00%c_FairValueInputsCommodityCorrelation
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
30.00%c_FairValueInputsCommodityCorrelation
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Forward price (as a percent) 98.00%c_FairValueInputsForwardPrice
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
101.74%c_FairValueInputsForwardPrice
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Equity-IR correlation (as a percent) 35.43%c_FairValueInputsEquityInterestRateCorrelation
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
35.43%c_FairValueInputsEquityInterestRateCorrelation
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_InterestBearingDepositsMember
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= us-gaap_WeightedAverageMember
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= c_ModelBasedValuationTechniqueMember
Federal funds purchased and securities loaned or sold under agreements to repurchase | Model-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Liabilities 1,060,000,000us-gaap_LiabilitiesFairValueDisclosure
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/ us-gaap_FairValueByLiabilityClassAxis
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= c_ModelBasedValuationTechniqueMember
1,043,000,000us-gaap_LiabilitiesFairValueDisclosure
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/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Federal funds purchased and securities loaned or sold under agreements to repurchase | Model-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Interest rate (as a percent) 0.87%c_FairValueInputsInterestRate
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= c_ModelBasedValuationTechniqueMember
0.74%c_FairValueInputsInterestRate
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= c_ModelBasedValuationTechniqueMember
Federal funds purchased and securities loaned or sold under agreements to repurchase | Model-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Interest rate (as a percent) 2.01%c_FairValueInputsInterestRate
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= us-gaap_FairValueInputsLevel3Member
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= c_ModelBasedValuationTechniqueMember
2.26%c_FairValueInputsInterestRate
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= us-gaap_MaximumMember
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= c_ModelBasedValuationTechniqueMember
Federal funds purchased and securities loaned or sold under agreements to repurchase | Model-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Interest rate (as a percent) 1.72%c_FairValueInputsInterestRate
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= us-gaap_FairValueInputsLevel3Member
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1.90%c_FairValueInputsInterestRate
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= us-gaap_WeightedAverageMember
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= c_ModelBasedValuationTechniqueMember
Trading account liabilities | Securities sold, not yet purchased | Model-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Liabilities 41,000,000us-gaap_LiabilitiesFairValueDisclosure
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251,000,000us-gaap_LiabilitiesFairValueDisclosure
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= us-gaap_SecuritiesSoldNotYetPurchasedMember
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= c_ModelBasedValuationTechniqueMember
Trading account liabilities | Securities sold, not yet purchased | Model-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Credit-IR correlation (as a percent)   (70.49%)c_FairValueInputsCreditInterestRateCorrelation
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= c_ModelBasedValuationTechniqueMember
Trading account liabilities | Securities sold, not yet purchased | Model-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Credit-IR correlation (as a percent)   8.81%c_FairValueInputsCreditInterestRateCorrelation
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Trading account liabilities | Securities sold, not yet purchased | Model-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Credit-IR correlation (as a percent)   47.17%c_FairValueInputsCreditInterestRateCorrelation
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/ us-gaap_FairValueByLiabilityClassAxis
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= c_ModelBasedValuationTechniqueMember
Trading account liabilities | Securities sold, not yet purchased | Price-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Liabilities 184,000,000us-gaap_LiabilitiesFairValueDisclosure
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= us-gaap_TradingLiabilitiesMember
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142,000,000us-gaap_LiabilitiesFairValueDisclosure
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= us-gaap_SecuritiesSoldNotYetPurchasedMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Trading account liabilities | Securities sold, not yet purchased | Price-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 0.00c_FairValueInputsPrice
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= us-gaap_FairValueInputsLevel3Member
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= us-gaap_TradingLiabilitiesMember
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0.00c_FairValueInputsPrice
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= us-gaap_MinimumMember
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= c_PriceBasedValuationTechniqueMember
Trading account liabilities | Securities sold, not yet purchased | Price-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 105.54c_FairValueInputsPrice
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
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117.00c_FairValueInputsPrice
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= c_PriceBasedValuationTechniqueMember
Trading account liabilities | Securities sold, not yet purchased | Price-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 33.74c_FairValueInputsPrice
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
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/ us-gaap_RangeAxis
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/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
70.33c_FairValueInputsPrice
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= c_PriceBasedValuationTechniqueMember
Short-term borrowings and long-term debt | Model-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Liabilities 7,309,000,000us-gaap_LiabilitiesFairValueDisclosure
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7,204,000,000us-gaap_LiabilitiesFairValueDisclosure
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= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Short-term borrowings and long-term debt | Model-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Credit correlation (as a percent) 87.50%c_FairValueInputsCreditCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
87.50%c_FairValueInputsCreditCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
IR lognormal volatility (as a percent)   18.05%c_FairValueInputsInterestRateLognormalVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Mean reversion (as a percent) 1.00%c_FairValueInputsMeanReversion
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
1.00%c_FairValueInputsMeanReversion
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Foreign exchange (FX) volatility (as a percent) 9.30%c_FairValueInputsForeignExchangeVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Equity volatility (as a percent) 15.41%c_FairValueInputsEquityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
10.18%c_FairValueInputsEquityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Equity forward (as a percent)   89.50%c_FairValueInputsEquityForward
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Equity-FX correlation (as a percent) (88.20%)c_FairValueInputsEquityForeignExchangeCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Equity-Equity correlation (as a percent) (66.30%)c_FairValueInputsEquityCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Commodity volatility (as a percent) 5.00%c_FairValueInputsCommodityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
5.00%c_FairValueInputsCommodityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Commodity correlation (as a percent) (52.00%)c_FairValueInputsCommodityCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
(57.00%)c_FairValueInputsCommodityCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Forward price (as a percent) 34.02%c_FairValueInputsForwardPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
35.34%c_FairValueInputsForwardPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Short-term borrowings and long-term debt | Model-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Credit correlation (as a percent) 87.50%c_FairValueInputsCreditCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
87.50%c_FairValueInputsCreditCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
IR lognormal volatility (as a percent)   90.65%c_FairValueInputsInterestRateLognormalVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Mean reversion (as a percent) 20.00%c_FairValueInputsMeanReversion
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
20.00%c_FairValueInputsMeanReversion
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Foreign exchange (FX) volatility (as a percent) 15.20%c_FairValueInputsForeignExchangeVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Equity volatility (as a percent) 32.00%c_FairValueInputsEquityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
69.65%c_FairValueInputsEquityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Equity forward (as a percent)   100.80%c_FairValueInputsEquityForward
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Equity-FX correlation (as a percent) 50.90%c_FairValueInputsEquityForeignExchangeCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Equity-Equity correlation (as a percent) 94.80%c_FairValueInputsEquityCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Commodity volatility (as a percent) 60.00%c_FairValueInputsCommodityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
83.00%c_FairValueInputsCommodityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Commodity correlation (as a percent) 91.00%c_FairValueInputsCommodityCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
91.00%c_FairValueInputsCommodityCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Forward price (as a percent) 242.86%c_FairValueInputsForwardPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
268.77%c_FairValueInputsForwardPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Short-term borrowings and long-term debt | Model-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Credit correlation (as a percent) 87.50%c_FairValueInputsCreditCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
87.50%c_FairValueInputsCreditCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
IR lognormal volatility (as a percent)   30.21%c_FairValueInputsInterestRateLognormalVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Mean reversion (as a percent) 10.50%c_FairValueInputsMeanReversion
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
10.50%c_FairValueInputsMeanReversion
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Foreign exchange (FX) volatility (as a percent) 14.41%c_FairValueInputsForeignExchangeVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Equity volatility (as a percent) 15.85%c_FairValueInputsEquityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
23.72%c_FairValueInputsEquityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Equity forward (as a percent)   95.80%c_FairValueInputsEquityForward
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Equity-FX correlation (as a percent) (38.24%)c_FairValueInputsEquityForeignExchangeCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Equity-Equity correlation (as a percent) 34.89%c_FairValueInputsEquityCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Commodity volatility (as a percent) 20.00%c_FairValueInputsCommodityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
24.00%c_FairValueInputsCommodityVolatility
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Commodity correlation (as a percent) 38.00%c_FairValueInputsCommodityCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
30.00%c_FairValueInputsCommodityCorrelation
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Forward price (as a percent) 94.40%c_FairValueInputsForwardPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
101.80%c_FairValueInputsForwardPrice
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByLiabilityClassAxis
= c_ShortTermAndLongTermDebtMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Federal funds sold and securities borrowed or purchased under agreements to resell | Model-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets 3,825,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
3,156,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Federal funds sold and securities borrowed or purchased under agreements to resell | Model-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Interest rate (as a percent) 1.09%c_FairValueInputsInterestRate
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
1.27%c_FairValueInputsInterestRate
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Credit-IR correlation (as a percent) (24.00%)c_FairValueInputsCreditInterestRateCorrelation
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Federal funds sold and securities borrowed or purchased under agreements to resell | Model-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Interest rate (as a percent) 1.58%c_FairValueInputsInterestRate
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
1.97%c_FairValueInputsInterestRate
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Credit-IR correlation (as a percent) (1.00%)c_FairValueInputsCreditInterestRateCorrelation
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Federal funds sold and securities borrowed or purchased under agreements to resell | Model-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Interest rate (as a percent) 1.56%c_FairValueInputsInterestRate
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
1.80%c_FairValueInputsInterestRate
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Credit-IR correlation (as a percent) (9.71%)c_FairValueInputsCreditInterestRateCorrelation
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Loans | Model-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets 964,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
832,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Loans | Model-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price   4.72c_FairValueInputsPrice
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Credit spread (as a percent) 0.39%c_FairValueInputsCreditSpread
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Loans | Model-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price   106.55c_FairValueInputsPrice
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Credit spread (as a percent) 6.00%c_FairValueInputsCreditSpread
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Loans | Model-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price   98.56c_FairValueInputsPrice
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
Credit spread (as a percent) 2.33%c_FairValueInputsCreditSpread
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_ModelBasedValuationTechniqueMember
 
Loans | Cash flow
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets 1,780,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
1,095,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
Loans | Cash flow | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 1.60%c_FairValueInputsYield
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
1.60%c_FairValueInputsYield
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
Loans | Cash flow | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 4.50%c_FairValueInputsYield
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
4.50%c_FairValueInputsYield
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
Loans | Cash flow | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 2.23%c_FairValueInputsYield
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
2.23%c_FairValueInputsYield
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
Loans | Price-based
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets 723,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
740,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Loans | Price-based | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Credit spread (as a percent)   0.35%c_FairValueInputsCreditSpread
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Appraised value 433,676,137c_FairValueInputsAppraisedValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
 
Loans | Price-based | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Credit spread (as a percent)   5.00%c_FairValueInputsCreditSpread
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Appraised value 433,676,137c_FairValueInputsAppraisedValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
 
Loans | Price-based | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Credit spread (as a percent)   1.99%c_FairValueInputsCreditSpread
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
Appraised value 433,676,137c_FairValueInputsAppraisedValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_PriceBasedValuationTechniqueMember
 
Loans | Yield analysis
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets 438,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ValuationTechniqueAxis
= c_YieldAnalysisValuationTechniqueMember
441,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ValuationTechniqueAxis
= c_YieldAnalysisValuationTechniqueMember
Loans | Yield analysis | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 0.00c_FairValueInputsPrice
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_YieldAnalysisValuationTechniqueMember
 
Loans | Yield analysis | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 131.31c_FairValueInputsPrice
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_YieldAnalysisValuationTechniqueMember
 
Loans | Yield analysis | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Price 63.60c_FairValueInputsPrice
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_YieldAnalysisValuationTechniqueMember
 
Mortgage servicing rights | Cash flow
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Total assets $ 1,590,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ServicingContractsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
$ 1,750,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ServicingContractsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
Mortgage servicing rights | Cash flow | Minimum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 4.81%c_FairValueInputsYield
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ServicingContractsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
5.19%c_FairValueInputsYield
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ServicingContractsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
WAL (in years) 3 years 2 months 26 days 3 years 3 months 22 days
Mortgage servicing rights | Cash flow | Maximum
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 23.64%c_FairValueInputsYield
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ServicingContractsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
21.40%c_FairValueInputsYield
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ServicingContractsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
WAL (in years) 7 years 5 months 13 days 7 years 10 months 21 days
Mortgage servicing rights | Cash flow | Weighted Average
   
Fair Value Inputs Assets Liabilities Quantitative Information    
Yield (as a percent) 7.33%c_FairValueInputsYield
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ServicingContractsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
10.25%c_FairValueInputsYield
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ServicingContractsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_ValuationTechniqueAxis
= c_CashflowValuationTechniqueMember
WAL (in years) 5 years 15 days 5 years 2 months 2 days