SECURITIES - Schedule of Investments (Details) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Securities Available-for-sale, Amortized Cost		$ 20,192	$ 19,713
Securities Available-for-sale, Gross Unrealized Gains		73	80
Securities Available-for-sale, Gross Unrealized Losses		(301)	(292)
Securities Available-for-sale, Fair Value	[1]	19,964	19,501
Securities Held-to-maturity, Amortized Cost		4,992	5,071
Securities Held-to-maturity, Gross Unrealized Gain		39	31
Securities Held-to-maturity, Gross Unrealized Losses		(36)	(44)
Securities held-to-maturity, Fair Value		4,995	5,058
Money market mutual fund, Amortized Cost		96	91
Money Market Mutual Fund, Gross Unrealized Gain		0	0
Money Market Mutual Fund, Gross Unrealized Loss		0	0
Money market mutual fund, Fair Value		96	91
Total other investment securities, at fair value, Amortized Cost		101	96
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		101	96
Other Investment Securities, at Cost, Amortized Cost		18	0
Other Investment Securities, at Cost, Gross Unrealized Gain		0	0
Other Investment Securities, at Cost, Gross Unrealized Loss		0	0
Other Investment Securities, at Cost, Fair Value		18	0
Total other investment securities, at cost		939	942
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		939	942
U.S. Treasury and other
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost		15	30
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		15	30
State and political subdivisions
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost		7	8
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		7	8
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		19,773	19,231
Debt Securities Available-for-sale, Gross Unrealized Gains		71	78
Debt Securities Available-for-sale, Gross Unrealized Losses		(282)	(264)
Debt Securities Available-for-sale, Fair Value		19,562	19,045
Securities Held-to-maturity, Amortized Cost		4,075	4,126
Securities Held-to-maturity, Gross Unrealized Gain		15	12
Securities Held-to-maturity, Gross Unrealized Losses		(36)	(44)
Securities held-to-maturity, Fair Value		4,054	4,094
Other/non-agency
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost		397	427
Debt Securities Available-for-sale, Gross Unrealized Gains		2	2
Debt Securities Available-for-sale, Gross Unrealized Losses		(19)	(28)
Debt Securities Available-for-sale, Fair Value		380	401
Securities Held-to-maturity, Amortized Cost		917	945
Securities Held-to-maturity, Gross Unrealized Gain		24	19
Securities Held-to-maturity, Gross Unrealized Losses		0	0
Securities held-to-maturity, Fair Value		941	964
Total mortgage-backed securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost		20,170	19,658
Debt Securities Available-for-sale, Gross Unrealized Gains		73	80
Debt Securities Available-for-sale, Gross Unrealized Losses		(301)	(292)
Debt Securities Available-for-sale, Fair Value		19,942	19,446
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		20,192	19,696
Debt Securities Available-for-sale, Gross Unrealized Gains		73	80
Debt Securities Available-for-sale, Gross Unrealized Losses		(301)	(292)
Debt Securities Available-for-sale, Fair Value		19,964	19,484
Marketable equity securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Equity Securities Available-for-sale, Amortized Cost		0	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		0	5
Other equity securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Equity Securities Available-for-sale, Amortized Cost		0	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		0	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		0	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		0	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		463	463
Federal Reserve Bank stock, Gross Unrealized Gains		0	0
Federal Reserve Bank stock, Gross Unrealized Losses		0	0
Federal Reserve Bank stock, Fair Value		463	463
Federal Home Loan Bank stock
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Federal Home Loan Bank stock, Amortized Cost		458	479
Federal Home Loan Bank stock, Gross Unrealized Gain		0	0
Federal Home Loan Bank stock, Gross Unrealized Losses		0	0
Federal Home Loan Bank stock, Fair Value		$ 458	$ 479

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