CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and due from banks	$ 23,967	$ 23,645
Cash and due from banks—intercompany	0	0
Deposits with banks	169,952	164,460
Deposits with banks—intercompany	0	0
Securities borrowed and purchased under resale agreements	251,322	270,684
Securities borrowed and purchased under resale agreements—intercompany	0	0
Trading account assets	276,140	256,117
Trading account assets—intercompany	0	0
Investments	368,563	358,607
Loans, net of unearned income	699,483	684,196
Loans, net of unearned income—intercompany	0	0
Allowance for loan losses	(12,783)	(12,315)	$ (12,355)	$ (12,060)
Total loans, net	686,700	671,881
Advances to subsidiaries	0	0
Investments in subsidiaries	0	0
Other assets	174,514	171,989
Other assets—intercompany	0	0
Total assets	1,951,158	1,917,383
Liabilities and equity
Deposits	1,070,590	1,013,170
Deposits—intercompany	0	0
Federal funds purchased and securities loaned or sold under agreements to repurchase, at fair value	166,339	177,768
Securities loaned and sold under repurchase agreements—intercompany	0	0
Trading account liabilities	119,894	144,305
Trading account liabilities—intercompany	0	0
Short-term borrowings	45,049	32,346
Short-term borrowings—intercompany	0	0
Long-term debt	248,760	231,999
Long-term debt—intercompany	0	0
Advances from subsidiaries	0	0
Other liabilities	106,580	120,721
Other liabilities—intercompany	0	0
Stockholders’ equity	193,946	197,074	$ 201,672
Total liabilities and equity	1,951,158	1,917,383
Other assets	107,709	109,273
Consolidating adjustments
Assets
Cash and due from banks	0	0
Cash and due from banks—intercompany	0	0
Deposits with banks	0	0
Deposits with banks—intercompany	0	0
Securities borrowed and purchased under resale agreements	0	0
Securities borrowed and purchased under resale agreements—intercompany	0	0
Trading account assets	0	0
Trading account assets—intercompany	0	0
Investments	0	0
Loans, net of unearned income	0	0
Loans, net of unearned income—intercompany	0	0
Allowance for loan losses	0	0
Total loans, net	0	0
Advances to subsidiaries	0	0
Investments in subsidiaries	(202,116)	(205,337)
Other assets	0	0
Other assets—intercompany	0	0
Total assets	(202,116)	(205,337)
Liabilities and equity
Deposits	0	0
Deposits—intercompany	0	0
Federal funds purchased and securities loaned or sold under agreements to repurchase, at fair value	0	0
Securities loaned and sold under repurchase agreements—intercompany	0	0
Trading account liabilities	0	0
Trading account liabilities—intercompany	0	0
Short-term borrowings	0	0
Short-term borrowings—intercompany	0	0
Long-term debt	0	0
Long-term debt—intercompany	0	0
Advances from subsidiaries	0	0
Other liabilities	0	0
Other liabilities—intercompany	0	0
Stockholders’ equity	(202,116)	(205,337)
Total liabilities and equity	(202,116)	(205,337)
Citigroup parent company
Liabilities and equity
Long-term debt	150,477
Other assets	35,100	34,700
Citigroup parent company | Reportable legal entities
Assets
Cash and due from banks	0	1
Cash and due from banks—intercompany	21	19
Deposits with banks	0	0
Deposits with banks—intercompany	3,000	3,000
Securities borrowed and purchased under resale agreements	0	0
Securities borrowed and purchased under resale agreements—intercompany	0	0
Trading account assets	286	302
Trading account assets—intercompany	426	627
Investments	1	7
Loans, net of unearned income	0	0
Loans, net of unearned income—intercompany	0	0
Allowance for loan losses	0	0
Total loans, net	0	0
Advances to subsidiaries	144,587	143,119
Investments in subsidiaries	202,116	205,337
Other assets	12,377	9,861
Other assets—intercompany	2,799	3,037
Total assets	365,613	365,310
Liabilities and equity
Deposits	0	0
Deposits—intercompany	0	0
Federal funds purchased and securities loaned or sold under agreements to repurchase, at fair value	0	0
Securities loaned and sold under repurchase agreements—intercompany	0	0
Trading account liabilities	1	1
Trading account liabilities—intercompany	379	410
Short-term borrowings	66	207
Short-term borrowings—intercompany	0	0
Long-term debt	150,477	143,767
Long-term debt—intercompany	0	0
Advances from subsidiaries	20,503	21,471
Other liabilities	937	3,011
Other liabilities—intercompany	8	223
Stockholders’ equity	193,242	196,220
Total liabilities and equity	365,613	365,310
CGMHI | Reportable legal entities
Assets
Cash and due from banks	586	689
Cash and due from banks—intercompany	5,095	3,545
Deposits with banks	4,050	4,915
Deposits with banks—intercompany	6,710	6,528
Securities borrowed and purchased under resale agreements	195,537	212,720
Securities borrowed and purchased under resale agreements—intercompany	21,446	20,074
Trading account assets	152,115	146,233
Trading account assets—intercompany	5,858	1,728
Investments	541	224
Loans, net of unearned income	2,497	1,292
Loans, net of unearned income—intercompany	0	0
Allowance for loan losses	0	0
Total loans, net	2,497	1,292
Advances to subsidiaries	0	0
Investments in subsidiaries	0	0
Other assets	54,784	59,734
Other assets—intercompany	45,588	44,255
Total assets	494,807	501,937
Liabilities and equity
Deposits	0	0
Deposits—intercompany	0	0
Federal funds purchased and securities loaned or sold under agreements to repurchase, at fair value	145,473	155,830
Securities loaned and sold under repurchase agreements—intercompany	36,581	21,109
Trading account liabilities	80,100	95,571
Trading account liabilities—intercompany	5,109	1,398
Short-term borrowings	11,096	3,656
Short-term borrowings—intercompany	17,129	11,343
Long-term debt	39,578	25,986
Long-term debt—intercompany	66,791	73,884
Advances from subsidiaries	0	0
Other liabilities	51,777	66,732
Other liabilities—intercompany	8,414	13,763
Stockholders’ equity	32,759	32,665
Total liabilities and equity	494,807	501,937
Other Citigroup subsidiaries and eliminations | Reportable legal entities
Assets
Cash and due from banks	23,381	22,955
Cash and due from banks—intercompany	(5,116)	(3,564)
Deposits with banks	165,902	159,545
Deposits with banks—intercompany	(9,710)	(9,528)
Securities borrowed and purchased under resale agreements	55,785	57,964
Securities borrowed and purchased under resale agreements—intercompany	(21,446)	(20,074)
Trading account assets	123,739	109,582
Trading account assets—intercompany	(6,284)	(2,355)
Investments	368,021	358,376
Loans, net of unearned income	696,986	682,904
Loans, net of unearned income—intercompany	0	0
Allowance for loan losses	(12,783)	(12,315)
Total loans, net	684,203	670,589
Advances to subsidiaries	(144,587)	(143,119)
Investments in subsidiaries	0	0
Other assets	107,353	102,394
Other assets—intercompany	(48,387)	(47,292)
Total assets	1,292,854	1,255,473
Liabilities and equity
Deposits	1,070,590	1,013,170
Deposits—intercompany	0	0
Federal funds purchased and securities loaned or sold under agreements to repurchase, at fair value	20,866	21,938
Securities loaned and sold under repurchase agreements—intercompany	(36,581)	(21,109)
Trading account liabilities	39,793	48,733
Trading account liabilities—intercompany	(5,488)	(1,808)
Short-term borrowings	33,887	28,483
Short-term borrowings—intercompany	(17,129)	(11,343)
Long-term debt	58,705	62,246
Long-term debt—intercompany	(66,791)	(73,884)
Advances from subsidiaries	(20,503)	(21,471)
Other liabilities	53,866	50,978
Other liabilities—intercompany	(8,422)	(13,986)
Stockholders’ equity	170,061	173,526
Total liabilities and equity	1,292,854	1,255,473
Up to 30 days | Citigroup parent company
Liabilities and equity
Placements with term of less than 30 days	$ 24,900	$ 22,400