CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities of continuing operations		$ 28,334	$ 41,364
Cash flows from investing activities of continuing operations
Purchases of investments		(155,804)	(195,421)
Proceeds from sales of investments		99,172	113,953
Proceeds from maturities of investments		52,607	64,850
Change in deposits with banks		(20,374)	(10,250)
Change in loans		(42,163)	(7,158)
Proceeds from sales and securitizations of loans		12,676	8,127
Proceeds from significant disposals	[1]	265	0
Change in federal funds sold and resales		(16,370)	10,875
Changes in investments and advances—intercompany		0	0
Other investing activities		(1,625)	(2,001)
Net cash used in investing activities of continuing operations		(71,616)	(17,025)
Cash flows from financing activities of continuing operations
Dividends paid		(1,517)	(838)
Issuance of preferred stock		2,498	4,731
Treasury stock acquired		(5,167)	(3,800)
Proceeds (repayments) from issuance of long-term debt, net		3,003	2,041
Proceeds (repayments) from issuance of long-term debt—intercompany, net		0	0
Change in deposits		32,365	4,911
Change in federal funds purchased and repos		6,628	(4,834)
Change in short-term borrowings		8,448	(35,756)
Net change in short-term borrowings and other advances—intercompany		0	0
Capital contributions from parent		0
Other financing activities		(313)	(425)
Net cash provided by (used in) financing activities of continuing operations		45,945	(33,970)
Effect of exchange rate changes on cash and cash equivalents		(144)	(751)
Change in cash and due from banks		2,519	(10,382)
Cash and due from banks at beginning of period		20,900	32,108
Cash and due from banks at end of period		23,419	21,726
Supplemental disclosure of cash flow information for continuing operations
Cash paid during the period for income taxes		2,855	4,043
Cash paid during the period for interest		9,760	8,441
Non-cash investing activities
Decrease in net loans associated with significant disposals reclassified to HFS		0	(9,063)
Decrease in investments associated with significant disposals reclassified to HFS		0	(1,402)
Decrease in goodwill and intangible assets associated with significant disposals reclassified to HFS		0	216
Decrease in deposits with banks associated with significant disposals reclassified to HFS		0	404
Transfers to loans HFS from loans		7,900	17,900
Transfers to OREO and other repossessed assets		138	225
Non-cash financing activities
Decrease in long-term debt associated with significant disposals reclassified to HFS		0	(6,179)
Reportable legal entities | Citigroup parent company
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities of continuing operations		16,685	14,915
Cash flows from investing activities of continuing operations
Purchases of investments		0	0
Proceeds from sales of investments		229	0
Proceeds from maturities of investments		61	210
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
Change in federal funds sold and resales		0	0
Changes in investments and advances—intercompany		(14,378)	(22,517)
Other investing activities		2,962	1
Net cash used in investing activities of continuing operations		(11,126)	(22,306)
Cash flows from financing activities of continuing operations
Dividends paid		(1,517)	(838)
Issuance of preferred stock		2,498	4,731
Treasury stock acquired		(5,167)	(3,800)
Proceeds (repayments) from issuance of long-term debt, net		1,613	8,683
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		(163)	(529)
Net change in short-term borrowings and other advances—intercompany		(2,503)	(434)
Capital contributions from parent		0
Other financing activities		(313)	(425)
Net cash provided by (used in) financing activities of continuing operations		(5,552)	7,388
Effect of exchange rate changes on cash and cash equivalents		0	0
Change in cash and due from banks		7	(3)
Cash and due from banks at beginning of period		124	125
Cash and due from banks at end of period		131	122
Supplemental disclosure of cash flow information for continuing operations
Cash paid during the period for income taxes		(265)	88
Cash paid during the period for interest		3,402	3,759
Non-cash investing activities
Decrease in net loans associated with significant disposals reclassified to HFS			0
Decrease in investments associated with significant disposals reclassified to HFS			0
Decrease in goodwill and intangible assets associated with significant disposals reclassified to HFS			0
Decrease in deposits with banks 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
Non-cash financing activities
Decrease in long-term debt associated with significant disposals reclassified to HFS			0
Reportable legal entities | CGMHI
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities of continuing operations		5,285	(1,849)
Cash flows from investing activities of continuing operations
Purchases of investments		0	(4)
Proceeds from sales of investments		0	53
Proceeds from maturities of investments		0	0
Change in deposits with banks		(1,464)	(10,267)
Change in loans		0	0
Proceeds from sales and securitizations of loans		0	0
Proceeds from significant disposals		0
Change in federal funds sold and resales		(12,398)	4,628
Changes in investments and advances—intercompany		(23)	2,207
Other investing activities		0	(63)
Net cash used in investing activities of continuing operations		(13,885)	(3,446)
Cash flows from financing activities of continuing operations
Dividends paid		0	0
Issuance of preferred stock		0	0
Treasury stock acquired		0	0
Proceeds (repayments) from issuance of long-term debt, net		4,196	(98)
Proceeds (repayments) from issuance of long-term debt—intercompany, net		(12,533)	12,514
Change in deposits		0	0
Change in federal funds purchased and repos		12,251	(5,956)
Change in short-term borrowings		1,251	(1,752)
Net change in short-term borrowings and other advances—intercompany		(726)	335
Capital contributions from parent		5,000
Other financing activities		0	0
Net cash provided by (used in) financing activities of continuing operations		9,439	5,043
Effect of exchange rate changes on cash and cash equivalents		0	0
Change in cash and due from banks		839	(252)
Cash and due from banks at beginning of period		1,995	1,751
Cash and due from banks at end of period		2,834	1,499
Supplemental disclosure of cash flow information for continuing operations
Cash paid during the period for income taxes		81	157
Cash paid during the period for interest		2,378	1,704
Non-cash investing activities
Decrease in net loans associated with significant disposals reclassified to HFS			0
Decrease in investments associated with significant disposals reclassified to HFS			0
Decrease in goodwill and intangible assets associated with significant disposals reclassified to HFS			0
Decrease in deposits with banks 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
Non-cash financing activities
Decrease in long-term debt associated with significant disposals reclassified to HFS			0
Reportable legal entities | Other Citigroup subsidiaries and eliminations
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities of continuing operations		6,364	28,298
Cash flows from investing activities of continuing operations
Purchases of investments		(155,804)	(195,417)
Proceeds from sales of investments		98,943	113,900
Proceeds from maturities of investments		52,546	64,640
Change in deposits with banks		(18,910)	17
Change in loans		(42,163)	(7,158)
Proceeds from sales and securitizations of loans		12,676	8,127
Proceeds from significant disposals		265
Change in federal funds sold and resales		(3,972)	6,247
Changes in investments and advances—intercompany		14,401	20,310
Other investing activities		(4,587)	(1,939)
Net cash used in investing activities of continuing operations		(46,605)	8,727
Cash flows from financing activities of continuing operations
Dividends paid		0	0
Issuance of preferred stock		0	0
Treasury stock acquired		0	0
Proceeds (repayments) from issuance of long-term debt, net		(2,806)	(6,544)
Proceeds (repayments) from issuance of long-term debt—intercompany, net		12,533	(12,514)
Change in deposits		32,365	4,911
Change in federal funds purchased and repos		(5,623)	1,122
Change in short-term borrowings		7,360	(33,475)
Net change in short-term borrowings and other advances—intercompany		3,229	99
Capital contributions from parent		(5,000)
Other financing activities		0	0
Net cash provided by (used in) financing activities of continuing operations		42,058	(46,401)
Effect of exchange rate changes on cash and cash equivalents		(144)	(751)
Change in cash and due from banks		1,673	(10,127)
Cash and due from banks at beginning of period		18,781	30,232
Cash and due from banks at end of period		20,454	20,105
Supplemental disclosure of cash flow information for continuing operations
Cash paid during the period for income taxes		3,039	3,798
Cash paid during the period for interest		3,980	2,978
Non-cash investing activities
Decrease in net loans associated with significant disposals reclassified to HFS			(9,063)
Decrease in investments associated with significant disposals reclassified to HFS			(1,402)
Decrease in goodwill and intangible assets associated with significant disposals reclassified to HFS			216
Decrease in deposits with banks associated with significant disposals reclassified to HFS			404
Transfers to loans HFS from loans		7,900	17,900
Transfers to OREO and other repossessed assets		138	225
Non-cash financing activities
Decrease in long-term debt associated with significant disposals reclassified to HFS			(6,179)
Consolidating adjustments
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by 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
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	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 (used in) 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 net loans associated with significant disposals reclassified to HFS			0
Decrease in investments associated with significant disposals reclassified to HFS			0
Decrease in goodwill and intangible assets associated with significant disposals reclassified to HFS			0
Decrease in deposits with banks 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
Non-cash financing activities
Decrease in long-term debt associated with significant disposals reclassified to HFS			$ 0

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