SECURITIES - Schedule of Investments (Details) - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Securities Available-for-sale, Amortized Cost		$ 17,715	$ 17,831
Securities Available-for-sale, Gross Unrealized Gains		302	157
Securities Available-for-sale, Gross Unrealized Losses		(53)	(104)
Securities Available-for-sale, Fair Value	[1]	17,964	17,884
Securities Held-to-maturity, Amortized Cost	[1]	5,129	5,258
Securities Held-to-maturity, Gross Unrealized Gain		132	50
Securities Held-to-maturity, Gross Unrealized Losses		0	(11)
Securities held-to-maturity, Fair Value		5,261	5,297
Money market mutual fund, Amortized Cost		63	65
Money market mutual fund, Gross Unrealized Gains		0	0
Money market mutual fund, Gross Unrealized Losses		0	0
Money market mutual fund, Fair Value		63	65
Total other investment securities, at fair value, Amortized Cost		68	70
Total other investments securities, at fair value, at cost, Gross Unrealized Gains		0	0
Total other investments securities, at fair value, Gross Unrealized Losses		0	0
Total other investment securities, at fair value, Fair Value		68	70
Total other investment securities, at cost		896	863
Total other investment securities, at cost, Gross Unrealized Gain		0	0
Total other investment securities, at cost, Gross Unrealized Losses		0	0
Total other investment securities, at cost, Fair Value		896	863
U.S. Treasury and other
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost		16	16
Debt Securities Available-for-sale, Gross Unrealized Gains		0	0
Debt Securities Available-for-sale, Gross Unrealized Losses		0	0
Debt Securities Available-for-sale, Fair Value		16	16
State and political subdivisions
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost		9	9
Debt Securities Available-for-sale, Gross Unrealized Gains		0	0
Debt Securities Available-for-sale, Gross Unrealized Losses		0	0
Debt Securities Available-for-sale, Fair Value		9	9
Federal agencies and U.S. government sponsored entities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost		17,147	17,234
Debt Securities Available-for-sale, Gross Unrealized Gains		300	153
Debt Securities Available-for-sale, Gross Unrealized Losses		(13)	(67)
Debt Securities Available-for-sale, Fair Value		17,434	17,320
Securities Held-to-maturity, Amortized Cost		4,010	4,105
Securities Held-to-maturity, Gross Unrealized Gain		93	27
Securities Held-to-maturity, Gross Unrealized Losses		0	(11)
Securities held-to-maturity, Fair Value		4,103	4,121
Other/non-agency
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost		526	555
Debt Securities Available-for-sale, Gross Unrealized Gains		2	4
Debt Securities Available-for-sale, Gross Unrealized Losses		(40)	(37)
Debt Securities Available-for-sale, Fair Value		488	522
Securities Held-to-maturity, Amortized Cost		1,119	1,153
Securities Held-to-maturity, Gross Unrealized Gain		39	23
Securities Held-to-maturity, Gross Unrealized Losses		0	0
Securities held-to-maturity, Fair Value		1,158	1,176
Total mortgage-backed securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost		17,673	17,789
Debt Securities Available-for-sale, Gross Unrealized Gains		302	157
Debt Securities Available-for-sale, Gross Unrealized Losses		(53)	(104)
Debt Securities Available-for-sale, Fair Value		17,922	17,842
Total debt securities available for sale
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost		17,698	17,814
Debt Securities Available-for-sale, Gross Unrealized Gains		302	157
Debt Securities Available-for-sale, Gross Unrealized Losses		(53)	(104)
Debt Securities Available-for-sale, Fair Value		17,947	17,867
Marketable equity securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Equity Securities Available-for-sale, Amortized Cost		5	5
Equity Securities Available-for-sale, Gross Unrealized Gains		0	0
Equity Securities Available-for-sale, Gross Unrealized Losses		0	0
Equity Securities Available-for-sale, Fair Value		5	5
Other equity securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Equity Securities Available-for-sale, Amortized Cost		12	12
Equity Securities Available-for-sale, Gross Unrealized Gains		0	0
Equity Securities Available-for-sale, Gross Unrealized Losses		0	0
Equity Securities Available-for-sale, Fair Value		12	12
Total equity securities available for sale
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Equity Securities Available-for-sale, Amortized Cost		17	17
Equity Securities Available-for-sale, Gross Unrealized Gains		0	0
Equity Securities Available-for-sale, Gross Unrealized Losses		0	0
Equity Securities Available-for-sale, Fair Value		17	17
Other investments
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Other Investments, Amortized Cost		5	5
Other Investments, Gross Unrealized Gain		0	0
Other Investments, Gross Unrealized Loss		0	0
Other Investments, Fair Value		5	5
Federal Reserve Bank stock
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Federal Reserve Bank stock, Amortized Cost		468	468
Federal Reserve Bank stock, Gross Unrealized Gains		0	0
Federal Reserve Bank stock, Gross Unrealized Loss		0	0
Federal Reserve Bank stock, Fair Value		468	468
Federal Home Loan Bank stock
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Federal Home Loan Bank stock, Amortized Cost		428	395
Federal Home Loan Bank stock, Gross Unrealized Gain		0	0
Federal Home Loan Bank stock, Gross Unrealized Loss		0	0
Federal Home Loan Bank stock, Fair Value		$ 428	$ 395

[1] Includes only collateral pledged by the Company where counterparties have the right to sell or pledge the collateral.