SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Mortgage Securitizations (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Cash Flows Between Transferor and Transferee
Gains recognized on the securitization	$ 0
U.S. government-sponsored agency guaranteed | Citicorp
Cash Flows Between Transferor and Transferee
Proceeds from new securitizations	5,500,000,000	7,100,000,000
Contractual servicing fees received	0	100,000,000
Cash flows received on retained interests and other net cash flows	0	0
Gains recognized on the securitization	20,000,000	6,000,000
Key assumptions used in measuring fair value of retained interests at date of sale or securitization of mortgage receivables
Weighted average discount rate	6.90%	10.30%
Weighted average constant prepayment rate	18.50%	4.70%
Key assumptions used in measuring fair value related to transferor's continuing involvement
Weighted average discount rate	6.70%		8.00%
Weighted average constant prepayment rate	16.80%		14.70%
Sensitivity analysis of fair value of interests continued to be held by transferor
Carrying value of retained interests	2,078,000,000		2,224,000,000
Carrying value of retained interests, impact of 10% adverse change in discount rate	(54,000,000)		(64,000,000)
Carrying value of retained interests, impact of 20% adverse change in discount rate	(105,000,000)		(124,000,000)
Carrying value of retained interests, impact of 10% adverse change in constant prepayment rate	(95,000,000)		(86,000,000)
Carrying value of retained interests, impact of 20% adverse change in constant prepayment rate	(181,000,000)		(165,000,000)
U.S. government-sponsored agency guaranteed | Citicorp | Low end of range
Key assumptions used in measuring fair value of retained interests at date of sale or securitization of mortgage receivables
Discount rate	0.00%	0.00%
Constant prepayment rate	16.40%	0.00%
Weighted average life	3 years 6 months	0 years
Key assumptions used in measuring fair value related to transferor's continuing involvement
Discount rate	0.00%		0.00%
Constant prepayment rate	6.60%		6.00%
Weighted average life	0 years 6 months		0 years
U.S. government-sponsored agency guaranteed | Citicorp | High end of range
Key assumptions used in measuring fair value of retained interests at date of sale or securitization of mortgage receivables
Discount rate	8.00%	11.30%
Constant prepayment rate	34.90%	16.00%
Weighted average life	5 years 7 months 6 days	9 years 8 months 12 days
Key assumptions used in measuring fair value related to transferor's continuing involvement
Discount rate	20.90%		21.20%
Constant prepayment rate	42.70%		41.40%
Weighted average life	17 years 9 months 18 days		16 years
U.S. government-sponsored agency guaranteed | Citi Holdings
Cash Flows Between Transferor and Transferee
Proceeds from new securitizations	100,000,000	100,000,000
Contractual servicing fees received	100,000,000	0
Gains recognized on the securitization	22,000,000	8,000,000
Key assumptions used in measuring fair value related to transferor's continuing involvement
Weighted average discount rate	8.20%		13.70%
Weighted average constant prepayment rate	19.10%		23.90%
Sensitivity analysis of fair value of interests continued to be held by transferor
Carrying value of retained interests	110,000,000		150,000,000
Carrying value of retained interests, impact of 10% adverse change in discount rate	(4,000,000)		(5,000,000)
Carrying value of retained interests, impact of 20% adverse change in discount rate	(7,000,000)		(10,000,000)
Carrying value of retained interests, impact of 10% adverse change in constant prepayment rate	(7,000,000)		(7,000,000)
Carrying value of retained interests, impact of 20% adverse change in constant prepayment rate	(13,000,000)		(14,000,000)
U.S. government-sponsored agency guaranteed | Citi Holdings | Low end of range
Key assumptions used in measuring fair value related to transferor's continuing involvement
Discount rate	1.10%		1.90%
Constant prepayment rate	15.10%		20.40%
Weighted average life	4 years 2 months 12 days		3 years 3 months 18 days
U.S. government-sponsored agency guaranteed | Citi Holdings | High end of range
Key assumptions used in measuring fair value related to transferor's continuing involvement
Discount rate	19.40%		19.20%
Constant prepayment rate	23.60%		32.30%
Weighted average life	4 years 8 months 12 days		4 years 7 months 6 days
Mortgage securitizations - Non-agency-sponsored | Citicorp
Cash Flows Between Transferor and Transferee
Proceeds from new securitizations	3,600,000,000	1,600,000,000
Contractual servicing fees received	0	0
Cash flows received on retained interests and other net cash flows	0	0
Gains recognized on the securitization	16,000,000	4,000,000
Mortgage securitizations - Non-agency-sponsored | Citi Holdings
Cash Flows Between Transferor and Transferee
Proceeds from new securitizations	0	0
Contractual servicing fees received	0	0
Senior interests | Citicorp
Key assumptions used in measuring fair value of retained interests at date of sale or securitization of mortgage receivables
Discount rate	2.80%	1.40%
Weighted average discount rate	2.80%	1.40%
Constant prepayment rate	0.00%	0.00%
Weighted average constant prepayment rate	0.00%	0.00%
Anticipated net credit losses	40.00%	40.00%
Weighted average anticipated net credit losses	40.00%	40.00%
Weighted average life	9 years 8 months 12 days	2 years 7 months 6 days
Key assumptions used in measuring fair value related to transferor's continuing involvement
Weighted average discount rate	5.60%		4.90%
Weighted average constant prepayment rate	16.10%		10.10%
Weighted average anticipated net credit losses	48.90%		54.60%
Sensitivity analysis of fair value of interests continued to be held by transferor
Carrying value of retained interests	234,000,000		285,000,000
Carrying value of retained interests, impact of 10% adverse change in discount rate	(5,000,000)		(5,000,000)
Carrying value of retained interests, impact of 20% adverse change in discount rate	(9,000,000)		(9,000,000)
Carrying value of retained interests, impact of 10% adverse change in constant prepayment rate	(1,000,000)		(1,000,000)
Carrying value of retained interests, impact of 20% adverse change in constant prepayment rate	(2,000,000)		(2,000,000)
Carrying value of retained interests, impact of 10% adverse change in anticipated net credit losses	(3,000,000)		(2,000,000)
Carrying value of retained interests, impact of 20% adverse change in anticipated net credit losses	(4,000,000)		(3,000,000)
Senior interests | Citicorp | Low end of range
Key assumptions used in measuring fair value related to transferor's continuing involvement
Discount rate	1.10%		1.10%
Constant prepayment rate	2.60%		2.00%
Anticipated net credit losses	0.00%		0.00%
Weighted average life	3 months 18 days		3 months 18 days
Senior interests | Citicorp | High end of range
Key assumptions used in measuring fair value related to transferor's continuing involvement
Discount rate	18.50%		17.70%
Constant prepayment rate	100.00%		100.00%
Anticipated net credit losses	94.90%		92.40%
Weighted average life	13 years 2 months 12 days		14 years 4 months 24 days
Senior interests | Citi Holdings
Key assumptions used in measuring fair value related to transferor's continuing involvement
Discount rate	40.10%
Weighted average discount rate	40.10%		36.30%
Constant prepayment rate	21.50%
Weighted average constant prepayment rate	21.50%		16.60%
Anticipated net credit losses	0.50%
Weighted average anticipated net credit losses	0.50%		19.20%
Weighted average life	4 years 4 months 24 days
Sensitivity analysis of fair value of interests continued to be held by transferor
Carrying value of retained interests	15,000,000		25,000,000
Carrying value of retained interests, impact of 10% adverse change in discount rate	(1,000,000)		(2,000,000)
Carrying value of retained interests, impact of 20% adverse change in discount rate	(1,000,000)		(4,000,000)
Carrying value of retained interests, impact of 10% adverse change in constant prepayment rate	(2,000,000)		(2,000,000)
Carrying value of retained interests, impact of 20% adverse change in constant prepayment rate	(5,000,000)		(3,000,000)
Carrying value of retained interests, impact of 10% adverse change in anticipated net credit losses	(4,000,000)		(4,000,000)
Carrying value of retained interests, impact of 20% adverse change in anticipated net credit losses	(8,000,000)		(7,000,000)
Senior interests | Citi Holdings | Low end of range
Key assumptions used in measuring fair value related to transferor's continuing involvement
Discount rate			5.10%
Constant prepayment rate			6.70%
Anticipated net credit losses	0.30%
Weighted average life			3 years 10 months 24 days
Senior interests | Citi Holdings | High end of range
Key assumptions used in measuring fair value related to transferor's continuing involvement
Discount rate			47.10%
Constant prepayment rate			20.00%
Anticipated net credit losses	73.70%
Weighted average life			6 years 4 months 24 days
Subordinated interests | Citicorp
Key assumptions used in measuring fair value of retained interests at date of sale or securitization of mortgage receivables
Weighted average discount rate	3.00%	7.10%
Constant prepayment rate		6.10%
Weighted average constant prepayment rate	2.30%	6.10%
Weighted average anticipated net credit losses	37.90%	50.70%
Key assumptions used in measuring fair value related to transferor's continuing involvement
Weighted average discount rate	7.80%		8.20%
Weighted average constant prepayment rate	6.40%		7.20%
Weighted average anticipated net credit losses	53.80%		52.50%
Sensitivity analysis of fair value of interests continued to be held by transferor
Carrying value of retained interests	556,000,000		554,000,000
Carrying value of retained interests, impact of 10% adverse change in discount rate	(29,000,000)		(30,000,000)
Carrying value of retained interests, impact of 20% adverse change in discount rate	(55,000,000)		(57,000,000)
Carrying value of retained interests, impact of 10% adverse change in constant prepayment rate	(9,000,000)		(9,000,000)
Carrying value of retained interests, impact of 20% adverse change in constant prepayment rate	(18,000,000)		(18,000,000)
Carrying value of retained interests, impact of 10% adverse change in anticipated net credit losses	(9,000,000)		(9,000,000)
Carrying value of retained interests, impact of 20% adverse change in anticipated net credit losses	(17,000,000)		(16,000,000)
Subordinated interests | Citicorp | Low end of range
Key assumptions used in measuring fair value of retained interests at date of sale or securitization of mortgage receivables
Discount rate	0.00%	4.90%
Constant prepayment rate	0.00%
Anticipated net credit losses	0.00%	40.00%
Weighted average life	0 years	3 years
Key assumptions used in measuring fair value related to transferor's continuing involvement
Discount rate	2.20%		1.30%
Constant prepayment rate	0.50%		0.50%
Anticipated net credit losses	37.80%		13.70%
Weighted average life	0 years 6 months		0 years
Subordinated interests | Citicorp | High end of range
Key assumptions used in measuring fair value of retained interests at date of sale or securitization of mortgage receivables
Discount rate	4.40%	9.10%
Constant prepayment rate	3.30%
Anticipated net credit losses	55.90%	51.80%
Weighted average life	12 years 2 months 12 days	14 years 6 months
Key assumptions used in measuring fair value related to transferor's continuing involvement
Discount rate	19.50%		19.60%
Constant prepayment rate	16.50%		16.20%
Anticipated net credit losses	91.40%		83.80%
Weighted average life	25 years 1 month 6 days		24 years 4 months 24 days
Collateralized debt obligations (CDOs) | Citi Holdings
Sensitivity analysis of fair value of interests continued to be held by transferor
Carrying value of retained interests	6,000,000		6,000,000
Carrying value of retained interests, impact of 10% adverse change in discount rate	(1,000,000)		(1,000,000)
Carrying value of retained interests, impact of 20% adverse change in discount rate	(1,000,000)		(2,000,000)
Collateralized debt obligations (CDOs) | Citi Holdings | Low end of range
Key assumptions used in measuring fair value of retained interests at date of sale or securitization of mortgage receivables
Discount rate	44.80%		44.70%
Collateralized debt obligations (CDOs) | Citi Holdings | High end of range
Key assumptions used in measuring fair value of retained interests at date of sale or securitization of mortgage receivables
Discount rate	49.30%		49.20%
Collateralized loan obligations (CLOs) | Low end of range
Key assumptions used in measuring fair value of retained interests at date of sale or securitization of mortgage receivables
Discount rate	1.40%		1.40%
Collateralized loan obligations (CLOs) | High end of range
Key assumptions used in measuring fair value of retained interests at date of sale or securitization of mortgage receivables
Discount rate	1.60%		1.60%
Collateralized loan obligations (CLOs) | Citicorp
Sensitivity analysis of fair value of interests continued to be held by transferor
Carrying value of retained interests	1,537,000,000		1,539,000,000
Carrying value of retained interests, impact of 10% adverse change in discount rate	(8,000,000)		(9,000,000)
Carrying value of retained interests, impact of 20% adverse change in discount rate	(17,000,000)		(18,000,000)
Collateralized loan obligations (CLOs) | Citi Holdings
Key assumptions used in measuring fair value of retained interests at date of sale or securitization of mortgage receivables
Discount rate	0.00%
Sensitivity analysis of fair value of interests continued to be held by transferor
Carrying value of retained interests	0		10,000,000
Collateralized loan obligations (CLOs) | Citi Holdings | Low end of range
Key assumptions used in measuring fair value of retained interests at date of sale or securitization of mortgage receivables
Discount rate			4.50%
Collateralized loan obligations (CLOs) | Citi Holdings | High end of range
Key assumptions used in measuring fair value of retained interests at date of sale or securitization of mortgage receivables
Discount rate			5.00%
Asset-backed securities | Citicorp
Cash Flows Between Transferor and Transferee
Proceeds from new securitizations	$ 0	$ 500,000,000