CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Assets
Cash and due from banks	$ 22,889		$ 23,967
Cash and due from banks—intercompany	0		0
Deposits with banks	286,884		169,952
Deposits with banks—intercompany	0		0
Securities borrowed or purchased under agreements to resell	282,917		251,322
Securities borrowed and purchased under resale agreements—intercompany	0		0
Trading account assets	362,311		276,140
Trading account assets—intercompany	0		0
Investments	433,253		368,563
Loans, net of unearned income	685,292		699,483
Loans, net of unearned income—intercompany	0		0
Allowance for credit losses on loans (ACLL)	(26,420)	$ (20,841)	(12,783)	$ (12,466)	$ (12,329)	$ (12,315)
Total loans, net	658,872		686,700
Advances to subsidiaries	0		0
Investments in subsidiaries	0		0
Other assets	185,589		174,514
Other assets—intercompany	0		0
Total assets	2,232,715		1,951,158
Liabilities and equity
Deposits	1,233,660		1,070,590
Deposits—intercompany	0		0
Securities loaned and sold under agreements to repurchase (including $59,445 and $40,651 as of June 30, 2020 and December 31, 2019, respectively, at fair value)	215,722		166,339
Securities loaned and sold under repurchase agreements—intercompany	0		0
Trading account liabilities	149,264		119,894
Trading account liabilities—intercompany	0		0
Short-term borrowings	40,156		45,049
Short-term borrowings—intercompany	0		0
Long-term debt	279,775		248,760
Long-term debt—intercompany	0		0
Advances from subsidiaries	0		0
Other liabilities, including allowance	121,836		106,580
Other liabilities—intercompany	0		0
Stockholders’ equity	192,302		193,946	$ 198,110
Total liabilities and equity	2,232,715		1,951,158
Other	108,106		107,709
Citigroup parent company
Liabilities and equity
Long-term debt	169,036		150,477
Citibank, N.A.
Liabilities and equity
Other	34,400		35,100
Reportable legal entities | Citigroup parent company
Assets
Cash and due from banks	0		0
Cash and due from banks—intercompany	23		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	250		286
Trading account assets—intercompany	261		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	151,652		144,587
Investments in subsidiaries	205,625		202,116
Other assets	13,299		12,377
Other assets—intercompany	3,535		2,799
Total assets	377,646		365,613
Liabilities and equity
Deposits	0		0
Deposits—intercompany	0		0
Securities loaned and sold under agreements to repurchase (including $59,445 and $40,651 as of June 30, 2020 and December 31, 2019, respectively, at fair value)	0		0
Securities loaned and sold under repurchase agreements—intercompany	0		0
Trading account liabilities	11		1
Trading account liabilities—intercompany	141		379
Short-term borrowings	25		66
Short-term borrowings—intercompany	0		0
Long-term debt	169,036		150,477
Long-term debt—intercompany	0		0
Advances from subsidiaries	13,678		20,503
Other liabilities, including allowance	3,139		937
Other liabilities—intercompany	(6)		8
Stockholders’ equity	191,622		193,242
Total liabilities and equity	377,646		365,613
Reportable legal entities | CGMHI
Assets
Cash and due from banks	403		586
Cash and due from banks—intercompany	3,325		5,095
Deposits with banks	4,784		4,050
Deposits with banks—intercompany	8,145		6,710
Securities borrowed or purchased under agreements to resell	221,779		195,537
Securities borrowed and purchased under resale agreements—intercompany	24,679		21,446
Trading account assets	223,733		152,115
Trading account assets—intercompany	3,786		5,858
Investments	458		541
Loans, net of unearned income	2,922		2,497
Loans, net of unearned income—intercompany	0		0
Allowance for credit losses on loans (ACLL)	0		0
Total loans, net	2,922		2,497
Advances to subsidiaries	0		0
Investments in subsidiaries	0		0
Other assets	64,181		54,784
Other assets—intercompany	50,952		45,588
Total assets	609,147		494,807
Liabilities and equity
Deposits	0		0
Deposits—intercompany	0		0
Securities loaned and sold under agreements to repurchase (including $59,445 and $40,651 as of June 30, 2020 and December 31, 2019, respectively, at fair value)	199,525		145,473
Securities loaned and sold under repurchase agreements—intercompany	51,179		36,581
Trading account liabilities	100,338		80,100
Trading account liabilities—intercompany	2,745		5,109
Short-term borrowings	12,170		11,096
Short-term borrowings—intercompany	16,888		17,129
Long-term debt	44,874		39,578
Long-term debt—intercompany	76,880		66,791
Advances from subsidiaries	0		0
Other liabilities, including allowance	59,236		51,777
Other liabilities—intercompany	9,530		8,414
Stockholders’ equity	35,782		32,759
Total liabilities and equity	609,147		494,807
Reportable legal entities | Other Citigroup subsidiaries and eliminations
Assets
Cash and due from banks	22,486		23,381
Cash and due from banks—intercompany	(3,348)		(5,116)
Deposits with banks	282,100		165,902
Deposits with banks—intercompany	(11,145)		(9,710)
Securities borrowed or purchased under agreements to resell	61,138		55,785
Securities borrowed and purchased under resale agreements—intercompany	(24,679)		(21,446)
Trading account assets	138,328		123,739
Trading account assets—intercompany	(4,047)		(6,284)
Investments	432,794		368,021
Loans, net of unearned income	682,370		696,986
Loans, net of unearned income—intercompany	0		0
Allowance for credit losses on loans (ACLL)	(26,420)		(12,783)
Total loans, net	655,950		684,203
Advances to subsidiaries	(151,652)		(144,587)
Investments in subsidiaries	0		0
Other assets	108,109		107,353
Other assets—intercompany	(54,487)		(48,387)
Total assets	1,451,547		1,292,854
Liabilities and equity
Deposits	1,233,660		1,070,590
Deposits—intercompany	0		0
Securities loaned and sold under agreements to repurchase (including $59,445 and $40,651 as of June 30, 2020 and December 31, 2019, respectively, at fair value)	16,197		20,866
Securities loaned and sold under repurchase agreements—intercompany	(51,179)		(36,581)
Trading account liabilities	48,915		39,793
Trading account liabilities—intercompany	(2,886)		(5,488)
Short-term borrowings	27,961		33,887
Short-term borrowings—intercompany	(16,888)		(17,129)
Long-term debt	65,865		58,705
Long-term debt—intercompany	(76,880)		(66,791)
Advances from subsidiaries	(13,678)		(20,503)
Other liabilities, including allowance	59,461		53,866
Other liabilities—intercompany	(9,524)		(8,422)
Stockholders’ equity	170,523		170,061
Total liabilities and equity	1,451,547		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	(205,625)		(202,116)
Other assets	0		0
Other assets—intercompany	0		0
Total assets	(205,625)		(202,116)
Liabilities and equity
Deposits	0		0
Deposits—intercompany	0		0
Securities loaned and sold under agreements to repurchase (including $59,445 and $40,651 as of June 30, 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	(205,625)		(202,116)
Total liabilities and equity	(205,625)		(202,116)
Up to 30 days | Citibank, N.A.
Liabilities and equity
Placements with term of less than 30 days	$ 29,200		$ 24,900