FAIR VALUE MEASUREMENTS - Schedule of Fair Value Measurements (Details) - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Assets
Securities available for sale	[1]	$ 17,964	$ 17,884
Loans held for sale, at fair value		365	325
Derivative assets		1,192	807
Money market mutual fund		63	65
Other investments		5	5
Total other investment securities, at fair value		68	70
Total assets		19,589	19,086
Liabilities
Total derivative liabilities		971	666
Total liabilities		971	666
Interest rate swaps
Assets
Derivative assets		1,035	636
Liabilities
Total derivative liabilities		825	505
Foreign exchange contracts
Assets
Derivative assets		146	163
Liabilities
Total derivative liabilities		138	156
Other contracts
Assets
Derivative assets		11	8
Liabilities
Total derivative liabilities		8	5
Mortgage-backed securities
Assets
Securities available for sale		17,922	17,842
State and political subdivisions
Assets
Securities available for sale		9	9
Equity securities
Assets
Securities available for sale		17	17
U.S. Treasury and other
Assets
Securities available for sale		16	16
Residential loans held for sale
Assets
Loans held for sale, at fair value		292	268
Commercial loans held for sale
Assets
Loans held for sale, at fair value		73	57
Level 1
Assets
Securities available for sale		15	15
Loans held for sale, at fair value		0	0
Derivative assets		0	0
Money market mutual fund		63	65
Other investments		0	0
Total other investment securities, at fair value		63	65
Total assets		78	80
Liabilities
Total derivative liabilities		0	0
Total liabilities		0	0
Level 1 | Interest rate swaps
Assets
Derivative assets		0	0
Liabilities
Total derivative liabilities		0	0
Level 1 | Foreign exchange contracts
Assets
Derivative assets		0	0
Liabilities
Total derivative liabilities		0	0
Level 1 | Other contracts
Assets
Derivative assets		0	0
Liabilities
Total derivative liabilities		0	0
Level 1 | Mortgage-backed securities
Assets
Securities available for sale		0	0
Level 1 | State and political subdivisions
Assets
Securities available for sale		0	0
Level 1 | Equity securities
Assets
Securities available for sale		0	0
Level 1 | U.S. Treasury and other
Assets
Securities available for sale		15	15
Level 1 | Residential loans held for sale
Assets
Loans held for sale, at fair value		0	0
Level 1 | Commercial loans held for sale
Assets
Loans held for sale, at fair value		0	0
Level 2
Assets
Securities available for sale		17,949	17,869
Loans held for sale, at fair value		365	325
Derivative assets		1,192	807
Money market mutual fund		0	0
Other investments		5	5
Total other investment securities, at fair value		5	5
Total assets		19,511	19,006
Liabilities
Total derivative liabilities		971	666
Total liabilities		971	666
Level 2 | Interest rate swaps
Assets
Derivative assets		1,035	636
Liabilities
Total derivative liabilities		825	505
Level 2 | Foreign exchange contracts
Assets
Derivative assets		146	163
Liabilities
Total derivative liabilities		138	156
Level 2 | Other contracts
Assets
Derivative assets		11	8
Liabilities
Total derivative liabilities		8	5
Level 2 | Mortgage-backed securities
Assets
Securities available for sale		17,922	17,842
Level 2 | State and political subdivisions
Assets
Securities available for sale		9	9
Level 2 | Equity securities
Assets
Securities available for sale		17	17
Level 2 | U.S. Treasury and other
Assets
Securities available for sale		1	1
Level 2 | Residential loans held for sale
Assets
Loans held for sale, at fair value		292	268
Level 2 | Commercial loans held for sale
Assets
Loans held for sale, at fair value		73	57
Level 3
Assets
Securities available for sale		0	0
Loans held for sale, at fair value		0	0
Derivative assets		0	0
Money market mutual fund		0	0
Other investments		0	0
Total other investment securities, at fair value		0	0
Total assets		0	0
Liabilities
Total derivative liabilities		0	0
Total liabilities		0	0
Level 3 | Interest rate swaps
Assets
Derivative assets		0	0
Liabilities
Total derivative liabilities		0	0
Level 3 | Foreign exchange contracts
Assets
Derivative assets		0	0
Liabilities
Total derivative liabilities		0	0
Level 3 | Other contracts
Assets
Derivative assets		0	0
Liabilities
Total derivative liabilities		0	0
Level 3 | Mortgage-backed securities
Assets
Securities available for sale		0	0
Level 3 | State and political subdivisions
Assets
Securities available for sale		0	0
Level 3 | Equity securities
Assets
Securities available for sale		0	0
Level 3 | U.S. Treasury and other
Assets
Securities available for sale		0	0
Level 3 | Residential loans held for sale
Assets
Loans held for sale, at fair value		0	0
Level 3 | Commercial loans held for sale
Assets
Loans held for sale, at fair value		$ 0	$ 0

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