REGULATORY CAPITAL AND CITIGROUP, INC. PARENT COMPANY INFORMATION - Regulatory Capital Compliance (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Required minimum, Tier 1 common capital (as a percent)	4.00%
Required minimum, Tier 1 capital ratio (as a percent)	5.50%
Well capitalized minimum, Tier 1 capital ratio (as a percent)	6.00%
Required minimum, Total capital ratio (as a percent)	8.00%
Well capitalized minimum, Total capital ratio (as a percent)	10.00%
Required minimum, Leverage ratio (as a percent)	4.00%
Well capitalized minimum, Leverage ratio (as a percent)	5.00%
Dividends received from Citibank N.A.	$ 8,900,000,000	$ 12,200,000,000
Citigroup Inc.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Common	166,984,000,000
Tier 1 Capital	166,984,000,000
Total Capital	185,280,000,000
Risk-weighted assets	1,275,012,000,000
Quarterly adjusted average total assets	1,849,297,000,000
Tier one common capital ratio (as a percent)	13.10%
Tier 1 Capital ratio (as a percent)	13.10%
Total Capital ratio (as a percent)	14.53%
Leverage ratio (as a percent)	9.03%
Citibank, N.A.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Common	129,135,000,000
Tier 1 Capital	129,135,000,000
Total Capital	140,119,000,000
Risk-weighted assets	946,333,000,000
Quarterly adjusted average total assets	1,367,444,000,000
Tier one common capital ratio (as a percent)	13.65%
Tier 1 Capital ratio (as a percent)	13.65%
Total Capital ratio (as a percent)	14.81%
Leverage ratio (as a percent)	9.44%
Citigroup Global Markets Inc.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Net capital or equivalent	5,521,000,000
Excess over minimum requirement	4,376,000,000
Citigroup Global Markets Limited
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Net capital or equivalent	7,162,000,000
Excess over minimum requirement	$ 2,482,000,000

Amount of leverage assets as calculated in accordance with U.S. Federal regulatory capital standards.

No definition available.

Name:	c_LeverageAssets
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Dividends that Citigroup received from Citibank during the current period.

+ References

No definition available.

+ Details

Name:	c_ProceedsFromDividendsReceivedFromCitibank
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Tier 1 common capital, as defined by Supervisory Capital Assessment Program by U.S. banking regulators.

+ References

No definition available.

+ Details

Name:	c_TierOneCommonCapital
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Tier 1 common capital divided by risk weighted assets, as by Supervisory Capital Assessment Program by U.S. banking regulators.

+ References

No definition available.

+ Details

Name:	c_TierOneCommonCapitalRatio
Namespace Prefix:	c_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier One Common Capital Required for Capital Adequacy to Risk Weighted Assets

+ References

No definition available.

+ Details

Name:	c_TierOneCommonCapitalRequiredforCapitalAdequacytoRiskWeightedAssets
Namespace Prefix:	c_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of total capital as defined in the regulations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 948

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47304-110998

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1H

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1H

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 948

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47080-110998

+ Details

Name:	us-gaap_Capital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1H

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826

+ Details

Name:	us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

+ Details

Name:	us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Total Capital divided by risk weighted assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_CapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of net capital in excess of the minimum required net capital.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Rule 15c3

-Number 240

-Section 1

-Paragraph 1

-Subparagraph i

-Article 15c3

-Subsection a

+ Details

Name:	us-gaap_ExcessNetCapitalAt1500Percent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Net capital is equal to the net worth of the broker dealer, less certain items such as exchange memberships, carrying value of securities not readily marketable, haircuts on marketable securities in proprietary accounts, furniture and equipment and other illiquid assets as defined.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Rule 15c3

-Number 240

-Section 1

-Paragraph 1

-Subparagraph ii

-Article 15c3

-Subsection a

+ Details

Name:	us-gaap_NetCapital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of risk-weighted assets as calculated in accordance with U.S. Federal regulatory capital standards.

+ References

No definition available.

+ Details

Name:	us-gaap_RiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Leverage Capital divided by average assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Risk Based Capital as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 capital divided by risk weighted assets as defined by regulations.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	dei_LegalEntityAxis=c_CitibankNASubsidiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=c_CitigroupGlobalMarketsHoldingsIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=c_CitigroupGlobalMarketsLimitedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=us-gaap_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: