CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities of continuing operations		$ (3,006)	$ (538)
Cash flows from investing activities of continuing operations
Purchases of investments		(41,584)	(59,715)
Proceeds from sales of investments		29,456	39,268
Proceeds from maturities of investments		24,006	16,544
Change in deposits with banks		(20,322)	(23,852)
Change in loans		(7,953)	(5,057)
Proceeds from sales and securitizations of loans		3,191	1,247
Proceeds from significant disposals	[1]	2,732	265
Change in federal funds sold and resales		(6,116)	(5,418)
Changes in investments and advances—intercompany		0	0
Other investing activities		(653)	(472)
Net cash used in investing activities of continuing operations		(17,243)	(37,190)
Cash flows from financing activities of continuing operations
Dividends paid		(744)	(359)
Issuance of preferred stock		0	1,004
Treasury stock acquired		(1,858)	(1,312)
Proceeds (repayments) from issuance of long-term debt, net		(282)	2,623
Proceeds (repayments) from issuance of long-term debt—intercompany, net		0	0
Change in deposits		20,584	26,704
Change in federal funds purchased and repos		6,409	10,712
Change in short-term borrowings		(4,574)	(186)
Net change in short-term borrowings and other advances—intercompany		0	0
Capital contributions from parent			0
Other financing activities		(397)	(308)
Net cash provided by financing activities of continuing operations		19,138	38,878
Effect of exchange rate changes on cash and cash equivalents		340	190
Change in cash and due from banks		(771)	1,340
Cash and due from banks at beginning of period		23,043	20,900
Cash and due from banks at end of period		22,272	22,240
Supplemental disclosure of cash flow information for continuing operations
Cash paid during the period for income taxes		913	688
Cash paid during the period for interest		3,250	2,694
Non-cash investing activities
Decrease in goodwill associated with significant disposals reclassified to HFS		0	(30)
Transfers to loans HFS from loans		2,800	3,200
Transfers to OREO and other repossessed assets		30	56
Reportable legal entities | Citigroup parent company
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities of continuing operations		24,958	5,194
Cash flows from investing activities of continuing operations
Purchases of investments		0	0
Proceeds from sales of investments		116	0
Proceeds from maturities of investments		0	26
Change in deposits with banks		0	0
Change in loans		0	0
Proceeds from sales and securitizations of loans		0	0
Proceeds from significant disposals		0	0
Change in federal funds sold and resales		0	0
Changes in investments and advances—intercompany		(569)	(12,271)
Other investing activities		0	0
Net cash used in investing activities of continuing operations		(453)	(12,245)
Cash flows from financing activities of continuing operations
Dividends paid		(744)	(359)
Issuance of preferred stock			1,004
Treasury stock acquired		(1,858)	(1,312)
Proceeds (repayments) from issuance of long-term debt, net		(6,395)	2,448
Proceeds (repayments) from issuance of long-term debt—intercompany, net		0	0
Change in deposits		0	0
Change in federal funds purchased and repos		0	0
Change in short-term borrowings		0	(109)
Net change in short-term borrowings and other advances—intercompany		(14,901)	5,926
Capital contributions from parent			0
Other financing activities		(397)	(308)
Net cash provided by financing activities of continuing operations		(24,295)	7,290
Effect of exchange rate changes on cash and cash equivalents		0	0
Change in cash and due from banks		210	239
Cash and due from banks at beginning of period		142	124
Cash and due from banks at end of period		352	363
Supplemental disclosure of cash flow information for continuing operations
Cash paid during the period for income taxes		(139)	(231)
Cash paid during the period for interest		1,153	1,036
Non-cash investing activities
Decrease in goodwill associated with significant disposals reclassified to HFS			0
Transfers to loans HFS from loans		0	0
Transfers to OREO and other repossessed assets		0	0
Reportable legal entities | CGMHI
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities of continuing operations		(3,405)	(2,833)
Cash flows from investing activities of continuing operations
Purchases of investments		0	0
Proceeds from sales of investments		0	0
Proceeds from maturities of investments		0	0
Change in deposits with banks		6,514	(7,380)
Change in loans		0	0
Proceeds from sales and securitizations of loans		0	0
Proceeds from significant disposals		0	0
Change in federal funds sold and resales		(2,623)	(1,127)
Changes in investments and advances—intercompany		(5,007)	(6,052)
Other investing activities		0	0
Net cash used in investing activities of continuing operations		(1,116)	(14,559)
Cash flows from financing activities of continuing operations
Dividends paid		0	0
Issuance of preferred stock			0
Treasury stock acquired		0	0
Proceeds (repayments) from issuance of long-term debt, net		5,175	1,527
Proceeds (repayments) from issuance of long-term debt—intercompany, net		(12,506)	(2,692)
Change in deposits		0	0
Change in federal funds purchased and repos		1,266	12,077
Change in short-term borrowings		605	342
Net change in short-term borrowings and other advances—intercompany		8,938	3,711
Capital contributions from parent			2,500
Other financing activities		0	0
Net cash provided by financing activities of continuing operations		3,478	17,465
Effect of exchange rate changes on cash and cash equivalents		0	0
Change in cash and due from banks		(1,043)	73
Cash and due from banks at beginning of period		4,690	1,995
Cash and due from banks at end of period		3,647	2,068
Supplemental disclosure of cash flow information for continuing operations
Cash paid during the period for income taxes		64	20
Cash paid during the period for interest		822	637
Non-cash investing activities
Decrease in goodwill associated with significant disposals reclassified to HFS			0
Transfers to loans HFS from loans		0	0
Transfers to OREO and other repossessed assets		0	0
Reportable legal entities | Other Citigroup subsidiaries and eliminations
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities of continuing operations		(24,559)	(2,899)
Cash flows from investing activities of continuing operations
Purchases of investments		(41,584)	(59,715)
Proceeds from sales of investments		29,340	39,268
Proceeds from maturities of investments		24,006	16,518
Change in deposits with banks		(26,836)	(16,472)
Change in loans		(7,953)	(5,057)
Proceeds from sales and securitizations of loans		3,191	1,247
Proceeds from significant disposals		2,732	265
Change in federal funds sold and resales		(3,493)	(4,291)
Changes in investments and advances—intercompany		5,576	18,323
Other investing activities		(653)	(472)
Net cash used in investing activities of continuing operations		(15,674)	(10,386)
Cash flows from financing activities of continuing operations
Dividends paid		0	0
Issuance of preferred stock			0
Treasury stock acquired		0	0
Proceeds (repayments) from issuance of long-term debt, net		938	(1,352)
Proceeds (repayments) from issuance of long-term debt—intercompany, net		12,506	2,692
Change in deposits		20,584	26,704
Change in federal funds purchased and repos		5,143	(1,365)
Change in short-term borrowings		(5,179)	(419)
Net change in short-term borrowings and other advances—intercompany		5,963	(9,637)
Capital contributions from parent			(2,500)
Other financing activities		0	0
Net cash provided by financing activities of continuing operations		39,955	14,123
Effect of exchange rate changes on cash and cash equivalents		340	190
Change in cash and due from banks		62	1,028
Cash and due from banks at beginning of period		18,211	18,781
Cash and due from banks at end of period		18,273	19,809
Supplemental disclosure of cash flow information for continuing operations
Cash paid during the period for income taxes		988	899
Cash paid during the period for interest		1,275	1,021
Non-cash investing activities
Decrease in goodwill associated with significant disposals reclassified to HFS			(30)
Transfers to loans HFS from loans		2,800	3,200
Transfers to OREO and other repossessed assets		30	56
Consolidating adjustments
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities of continuing operations		0	0
Cash flows from investing activities of continuing operations
Purchases of investments		0	0
Proceeds from sales of investments		0	0
Proceeds from maturities of investments		0	0
Change in deposits with banks		0	0
Change in loans		0	0
Proceeds from sales and securitizations of loans		0	0
Proceeds from significant disposals		0	0
Change in federal funds sold and resales		0	0
Changes in investments and advances—intercompany		0	0
Other investing activities		0	0
Net cash used in investing activities of continuing operations		0	0
Cash flows from financing activities of continuing operations
Dividends paid		0	0
Issuance of preferred stock			0
Treasury stock acquired		0	0
Proceeds (repayments) from issuance of long-term debt, net		0	0
Proceeds (repayments) from issuance of long-term debt—intercompany, net		0	0
Change in deposits		0	0
Change in federal funds purchased and repos		0	0
Change in short-term borrowings		0	0
Net change in short-term borrowings and other advances—intercompany		0	0
Capital contributions from parent			0
Other financing activities		0	0
Net cash provided by financing activities of continuing operations		0	0
Effect of exchange rate changes on cash and cash equivalents		0	0
Change in cash and due from banks		0	0
Cash and due from banks at beginning of period		0	0
Cash and due from banks at end of period		0	0
Supplemental disclosure of cash flow information for continuing operations
Cash paid during the period for income taxes		0	0
Cash paid during the period for interest		0	0
Non-cash investing activities
Decrease in goodwill associated with significant disposals reclassified to HFS			0
Transfers to loans HFS from loans		0	0
Transfers to OREO and other repossessed assets		$ 0	$ 0

[1] See Note 2 to the Consolidated Financial Statements for further information on significant disposals.