RETIREMENT BENEFITS - Post Employment and Defined Contribution Plans (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Early Retiree Reinsurance Program
Reimbursements received under Early Retiree Reinsurance Program	$ 8,000,000
Reimbursements used to reduce health benefit costs		3,000,000	5,000,000
Defined Contribution Plans
Maximum percentage contribution by employer of employees eligible pay	6.00%
Maximum compensation to be eligible for fixed contribution from employer	100,000
Percentage of fixed contribution by employer, for eligible employees whose compensation is $100,000 or less	2.00%
Pretax expense associated with Citigroup 401(k) plan	383,000,000	394,000,000	384,000,000
U.S. Postretirement Benefit Plans
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0	0
Interest cost	33,000,000	33,000,000	44,000,000
Prior service cost (benefit)	0	(1,000,000)	(1,000,000)
Net actuarial loss	184,000,000	(253,000,000)
Total net (benefit) expense	32,000,000	30,000,000	43,000,000
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate (as a percent)	3.80%	4.35%
Health care cost increase following year (as percent)	7.50%	8.00%
Ultimate rate to which cost increase is assumed to decline (as percent)	5.00%	5.00%
Year in which the ultimate rate is reached	2020	2020
Postemployment Plans
Postemployment Plans
Funded status recognized	(256,000,000)	(252,000,000)
Amount in accumulated other comprehensive income (loss)	24,000,000	46,000,000
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	20,000,000	22,000,000
Interest cost	5,000,000	10,000,000	13,000,000
Prior service cost (benefit)	(31,000,000)	(3,000,000)	7,000,000
Net actuarial loss	14,000,000	17,000,000	13,000,000
Total service related expense	(12,000,000)	44,000,000	55,000,000
Non-service related expense (benefit)	37,000,000	(14,000,000)	24,000,000
Total net (benefit) expense	$ 25,000,000	$ 30,000,000	$ 79,000,000
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate (as a percent)	3.45%	4.05%
Health care cost increase following year (as percent)	7.50%	8.00%
Ultimate rate to which cost increase is assumed to decline (as percent)	5.00%	5.00%
Year in which the ultimate rate is reached	2020	2020

Represents the non-service related expense for defined benefit plans for the period.

No definition available.

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Represents the service related expense for defined benefit plans for the period.

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No definition available.

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Represents the maximum compensations of employees to be eligible to receive the fixed contributions from employer.

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No definition available.

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Represents the maximum percentage of fixed contribution for eligible employees whose compensation is 100,000 or less.

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Represents the amount of federal government reimbursements received during the period under the Early Retiree Health Reinsurance Program.

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No definition available.

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Represents the amount of federal government reimbursements received under the Early Retiree Health Reinsurance Program, used to reduce health benefit costs during the period.

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No definition available.

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- Definition

The total of net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost.

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- Definition

Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan.

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-Glossary Gain or Loss

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- Definition

The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.

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- Definition

The interest rate used to adjust for the time value of money for the plan.

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- Definition

The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

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- Definition

The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

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The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

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-Glossary Service Cost (Component of Net Periodic Pension Cost)

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The ultimate trend rate for health care costs.

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Year the ultimate health care cost trend rate is expected to be reached, in CCYY format.

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The amount of the cost recognized during the period for defined contribution plans.

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- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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No definition available.

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The carrying amount as of the balance sheet date of the obligations recognized for the various benefits provided to former or inactive employees, their beneficiaries, and covered dependents after employment but before retirement.

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