SECURITIES - Schedule of Investments (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Securities Available-for-sale, Amortized Cost	$ 17,968	$ 18,433
Securities Available-for-sale, Gross Unrealized Gains	295	308
Securities Available-for-sale, Gross Unrealized Losses	(66)	(85)
Securities Available-for-sale, Fair Value	18,197	18,656
Securities Held-to-maturity, Amortized Cost	5,285	5,148
Securities Held-to-maturity, Gross Unrealized Gain	105	76
Securities Held-to-maturity, Gross Unrealized Losses	(4)	(31)
Securities held-to-maturity, Fair Value	5,386	5,193
Money market mutual fund, Amortized Cost	45	28
Money market mutual fund, Gross Unrealized Gains	0	0
Money market mutual fund, Gross Unrealized Losses	0	0
Money market mutual fund, Fair Value	45	28
Total other investment securities, at fair value, Amortized Cost	50	33
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
Other investment securities, at fair value	50	33
Total other investment securities, at cost	822	867
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	822	867
U.S. Treasury
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost	15	15
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	15
State and political subdivisions
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost	9	10
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	10
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	17,340	17,683
Debt Securities Available-for-sale, Gross Unrealized Gains	292	301
Debt Securities Available-for-sale, Gross Unrealized Losses	(25)	(50)
Debt Securities Available-for-sale, Fair Value	17,607	17,934
Securities Held-to-maturity, Amortized Cost	4,092	3,728
Securities Held-to-maturity, Gross Unrealized Gain	67	22
Securities Held-to-maturity, Gross Unrealized Losses	(4)	(31)
Securities held-to-maturity, Fair Value	4,155	3,719
Other/non-agency
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost	587	703
Debt Securities Available-for-sale, Gross Unrealized Gains	3	4
Debt Securities Available-for-sale, Gross Unrealized Losses	(41)	(35)
Debt Securities Available-for-sale, Fair Value	549	672
Securities Held-to-maturity, Amortized Cost	1,193	1,420
Securities Held-to-maturity, Gross Unrealized Gain	38	54
Securities Held-to-maturity, Gross Unrealized Losses	0	0
Securities held-to-maturity, Fair Value	1,231	1,474
Total mortgage-backed securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost	17,927	18,386
Debt Securities Available-for-sale, Gross Unrealized Gains	295	305
Debt Securities Available-for-sale, Gross Unrealized Losses	(66)	(85)
Debt Securities Available-for-sale, Fair Value	18,156	18,606
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	17,951	18,411
Debt Securities Available-for-sale, Gross Unrealized Gains	295	305
Debt Securities Available-for-sale, Gross Unrealized Losses	(66)	(85)
Debt Securities Available-for-sale, Fair Value	18,180	18,631
Marketable equity securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Equity Securities Available-for-sale, Amortized Cost	5	10
Equity Securities Available-for-sale, Gross Unrealized Gains	0	3
Equity Securities Available-for-sale, Gross Unrealized Losses	0	0
Equity Securities Available-for-sale, Fair Value	5	13
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	22
Equity Securities Available-for-sale, Gross Unrealized Gains	0	3
Equity Securities Available-for-sale, Gross Unrealized Losses	0	0
Equity Securities Available-for-sale, Fair Value	17	25
Venture capital and other investments
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Venture Capital and Other Investments, Amortized Cost	5	5
Venture Capital and Other Investments, Gross Unrealized Gain	0	0
Venture Capital and Other Investments, Gross Unrealized Loss	0	0
Venture Capital and 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	477
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	477
Federal Home Loan Bank stock
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Federal Home Loan Bank stock, Amortized Cost	354	390
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	$ 354	$ 390