SECURITIES - Schedule of Investments (Details) - USD ($) $ in Millions		Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Securities Available-for-sale, Amortized Cost		$ 20,091	$ 19,713
Securities Available-for-sale, Gross Unrealized Gains		82	80
Securities Available-for-sale, Gross Unrealized Losses		(191)	(292)
Securities Available-for-sale, Fair Value	[1]	19,982	19,501
Securities Held-to-maturity, Amortized Cost		4,823	5,071
Securities Held-to-maturity, Gross Unrealized Gain		44	31
Securities Held-to-maturity, Gross Unrealized Losses		(28)	(44)
Securities held-to-maturity, Fair Value		4,839	5,058
Money market mutual fund, Amortized Cost		160	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		160	91
Total other investment securities, at fair value, Amortized Cost		165	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		165	96
Other Investment Securities, at Cost, Amortized Cost		7	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		7	0
Total other investment securities, at cost		772	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		772	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		12	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		12	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		19,735	19,231
Debt Securities Available-for-sale, Gross Unrealized Gains		76	78
Debt Securities Available-for-sale, Gross Unrealized Losses		(183)	(264)
Debt Securities Available-for-sale, Fair Value		19,628	19,045
Securities Held-to-maturity, Amortized Cost		3,966	4,126
Securities Held-to-maturity, Gross Unrealized Gain		18	12
Securities Held-to-maturity, Gross Unrealized Losses		(28)	(44)
Securities held-to-maturity, Fair Value		3,956	4,094
Other/non-agency
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost		337	427
Debt Securities Available-for-sale, Gross Unrealized Gains		6	2
Debt Securities Available-for-sale, Gross Unrealized Losses		(8)	(28)
Debt Securities Available-for-sale, Fair Value		335	401
Securities Held-to-maturity, Amortized Cost		857	945
Securities Held-to-maturity, Gross Unrealized Gain		26	19
Securities Held-to-maturity, Gross Unrealized Losses		0	0
Securities held-to-maturity, Fair Value		883	964
Total mortgage-backed securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost		20,072	19,658
Debt Securities Available-for-sale, Gross Unrealized Gains		82	80
Debt Securities Available-for-sale, Gross Unrealized Losses		(191)	(292)
Debt Securities Available-for-sale, Fair Value		19,963	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		20,091	19,696
Debt Securities Available-for-sale, Gross Unrealized Gains		82	80
Debt Securities Available-for-sale, Gross Unrealized Losses		(191)	(292)
Debt Securities Available-for-sale, Fair Value		19,982	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		302	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		$ 302	$ 479

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