CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Assets
Cash and due from banks	$ 23,755	$ 23,967
Cash and due from banks—intercompany	0	0
Deposits with banks	262,165	169,952
Deposits with banks—intercompany	0	0
Securities borrowed or purchased under agreements to resell	262,536	251,322
Securities borrowed and purchased under resale agreements—intercompany	0	0
Trading account assets	365,000	276,140
Trading account assets—intercompany	0	0
Investments	398,883	368,563
Loans, net of unearned income	721,020	699,483
Loans, net of unearned income—intercompany	0	0
Allowance for credit losses on loans (ACLL)	(20,841)	(12,783)	$ (12,329)	$ (12,315)
Total loans, net	700,179	686,700
Advances to subsidiaries	0	0
Investments in subsidiaries	0	0
Other assets	207,252	174,514
Other assets—intercompany	0	0
Total assets	2,219,770	1,951,158
Liabilities and equity
Deposits	1,184,911	1,070,590
Deposits—intercompany	0	0
Securities loaned and sold under agreements to repurchase (including $62,734 and $40,651 as of March 31, 2020 and December 31, 2019, respectively, at fair value)	222,324	166,339
Securities loaned and sold under repurchase agreements—intercompany	0	0
Trading account liabilities	163,995	119,894
Trading account liabilities—intercompany	0	0
Short-term borrowings	54,951	45,049
Short-term borrowings—intercompany	0	0
Long-term debt	266,098	248,760
Long-term debt—intercompany	0	0
Advances from subsidiaries	0	0
Other liabilities, including allowance	134,509	106,580
Other liabilities—intercompany	0	0
Stockholders’ equity	192,982	193,946	$ 197,015
Total liabilities and equity	2,219,770	1,951,158
Other	112,873	107,709
Citigroup parent company
Liabilities and equity
Long-term debt	156,461	150,477
Citibank, N.A.
Liabilities and equity
Other	43,300	35,100
Reportable legal entities | Citigroup parent company
Assets
Cash and due from banks	0	0
Cash and due from banks—intercompany	15	21
Deposits with banks	0	0
Deposits with banks—intercompany	3,000	3,000
Securities borrowed or purchased under agreements to resell	0	0
Securities borrowed and purchased under resale agreements—intercompany	0	0
Trading account assets	329	286
Trading account assets—intercompany	167	426
Investments	1	1
Loans, net of unearned income	0	0
Loans, net of unearned income—intercompany	0	0
Allowance for credit losses on loans (ACLL)	0	0
Total loans, net	0	0
Advances to subsidiaries	142,560	144,587
Investments in subsidiaries	204,662	202,116
Other assets	12,152	12,377
Other assets—intercompany	3,451	2,799
Total assets	366,337	365,613
Liabilities and equity
Deposits	0	0
Deposits—intercompany	0	0
Securities loaned and sold under agreements to repurchase (including $62,734 and $40,651 as of March 31, 2020 and December 31, 2019, respectively, at fair value)	0	0
Securities loaned and sold under repurchase agreements—intercompany	0	0
Trading account liabilities	0	1
Trading account liabilities—intercompany	445	379
Short-term borrowings	28	66
Short-term borrowings—intercompany	0	0
Long-term debt	156,461	150,477
Long-term debt—intercompany	0	0
Advances from subsidiaries	13,996	20,503
Other liabilities, including allowance	3,001	937
Other liabilities—intercompany	75	8
Stockholders’ equity	192,331	193,242
Total liabilities and equity	366,337	365,613
Reportable legal entities | CGMHI
Assets
Cash and due from banks	616	586
Cash and due from banks—intercompany	3,909	5,095
Deposits with banks	6,581	4,050
Deposits with banks—intercompany	8,392	6,710
Securities borrowed or purchased under agreements to resell	200,718	195,537
Securities borrowed and purchased under resale agreements—intercompany	24,686	21,446
Trading account assets	212,464	152,115
Trading account assets—intercompany	6,045	5,858
Investments	508	541
Loans, net of unearned income	1,722	2,497
Loans, net of unearned income—intercompany	0	0
Allowance for credit losses on loans (ACLL)	0	0
Total loans, net	1,722	2,497
Advances to subsidiaries	0	0
Investments in subsidiaries	0	0
Other assets	84,877	54,784
Other assets—intercompany	50,312	45,588
Total assets	600,830	494,807
Liabilities and equity
Deposits	0	0
Deposits—intercompany	0	0
Securities loaned and sold under agreements to repurchase (including $62,734 and $40,651 as of March 31, 2020 and December 31, 2019, respectively, at fair value)	201,631	145,473
Securities loaned and sold under repurchase agreements—intercompany	29,764	36,581
Trading account liabilities	104,146	80,100
Trading account liabilities—intercompany	5,421	5,109
Short-term borrowings	13,997	11,096
Short-term borrowings—intercompany	25,563	17,129
Long-term debt	37,118	39,578
Long-term debt—intercompany	65,945	66,791
Advances from subsidiaries	0	0
Other liabilities, including allowance	71,096	51,777
Other liabilities—intercompany	10,464	8,414
Stockholders’ equity	35,685	32,759
Total liabilities and equity	600,830	494,807
Reportable legal entities | Other Citigroup subsidiaries and eliminations
Assets
Cash and due from banks	23,139	23,381
Cash and due from banks—intercompany	(3,924)	(5,116)
Deposits with banks	255,584	165,902
Deposits with banks—intercompany	(11,392)	(9,710)
Securities borrowed or purchased under agreements to resell	61,818	55,785
Securities borrowed and purchased under resale agreements—intercompany	(24,686)	(21,446)
Trading account assets	152,207	123,739
Trading account assets—intercompany	(6,212)	(6,284)
Investments	398,374	368,021
Loans, net of unearned income	719,298	696,986
Loans, net of unearned income—intercompany	0	0
Allowance for credit losses on loans (ACLL)	(20,841)	(12,783)
Total loans, net	698,457	684,203
Advances to subsidiaries	(142,560)	(144,587)
Investments in subsidiaries	0	0
Other assets	110,223	107,353
Other assets—intercompany	(53,763)	(48,387)
Total assets	1,457,265	1,292,854
Liabilities and equity
Deposits	1,184,911	1,070,590
Deposits—intercompany	0	0
Securities loaned and sold under agreements to repurchase (including $62,734 and $40,651 as of March 31, 2020 and December 31, 2019, respectively, at fair value)	20,693	20,866
Securities loaned and sold under repurchase agreements—intercompany	(29,764)	(36,581)
Trading account liabilities	59,849	39,793
Trading account liabilities—intercompany	(5,866)	(5,488)
Short-term borrowings	40,926	33,887
Short-term borrowings—intercompany	(25,563)	(17,129)
Long-term debt	72,519	58,705
Long-term debt—intercompany	(65,945)	(66,791)
Advances from subsidiaries	(13,996)	(20,503)
Other liabilities, including allowance	60,412	53,866
Other liabilities—intercompany	(10,539)	(8,422)
Stockholders’ equity	169,628	170,061
Total liabilities and equity	1,457,265	1,292,854
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 or purchased under agreements to resell	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 credit losses on loans (ACLL)	0	0
Total loans, net	0	0
Advances to subsidiaries	0	0
Investments in subsidiaries	(204,662)	(202,116)
Other assets	0	0
Other assets—intercompany	0	0
Total assets	(204,662)	(202,116)
Liabilities and equity
Deposits	0	0
Deposits—intercompany	0	0
Securities loaned and sold under agreements to repurchase (including $62,734 and $40,651 as of March 31, 2020 and December 31, 2019, respectively, 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, including allowance	0	0
Other liabilities—intercompany	0	0
Stockholders’ equity	(204,662)	(202,116)
Total liabilities and equity	(204,662)	(202,116)
Up to 30 days | Citibank, N.A.
Liabilities and equity
Placements with term of less than 30 days	$ 38,100	$ 24,900