FAIR VALUE MEASUREMENTS - Schedule of Fair Value Measurements (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Assets
Securities available for sale	[1]	$ 17,884	$ 18,656
Loans held for sale		325	256
Derivative assets		807	790
Money market mutual fund		65	28
Other investments		5	5
Total other investment securities, at fair value		70	33
Total assets		19,086	19,735
Liabilities
Total derivative liabilities		666	773
Total liabilities		666	773
Interest rate swaps
Assets
Derivative assets		636	613
Liabilities
Total derivative liabilities		505	600
Foreign exchange contracts
Assets
Derivative assets		163	170
Liabilities
Total derivative liabilities		156	164
Other contracts
Assets
Derivative assets		8	7
Liabilities
Total derivative liabilities		5	9
Mortgage-backed securities
Assets
Securities available for sale		17,842	18,606
State and political subdivisions
Assets
Securities available for sale		9	10
Equity securities
Assets
Securities available for sale		17	25
U.S. Treasury and other
Assets
Securities available for sale		16	15
Residential loans held for sale
Assets
Loans held for sale		268	213
Commercial real estate loans held for sale
Assets
Loans held for sale		57	43
Level 1
Assets
Securities available for sale		15	23
Loans held for sale		0	0
Derivative assets		0	0
Money market mutual fund		65	28
Other investments		0	0
Total other investment securities, at fair value		65	28
Total assets		80	51
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	8
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		0	0
Level 1 | Commercial real estate loans held for sale
Assets
Loans held for sale		0	0
Level 2
Assets
Securities available for sale		17,869	18,633
Loans held for sale		325	256
Derivative assets		807	790
Money market mutual fund		0	0
Other investments		5	0
Total other investment securities, at fair value		5	0
Total assets		19,006	19,679
Liabilities
Total derivative liabilities		666	773
Total liabilities		666	773
Level 2 | Interest rate swaps
Assets
Derivative assets		636	613
Liabilities
Total derivative liabilities		505	600
Level 2 | Foreign exchange contracts
Assets
Derivative assets		163	170
Liabilities
Total derivative liabilities		156	164
Level 2 | Other contracts
Assets
Derivative assets		8	7
Liabilities
Total derivative liabilities		5	9
Level 2 | Mortgage-backed securities
Assets
Securities available for sale		17,842	18,606
Level 2 | State and political subdivisions
Assets
Securities available for sale		9	10
Level 2 | Equity securities
Assets
Securities available for sale		17	17
Level 2 | U.S. Treasury and other
Assets
Securities available for sale		1	0
Level 2 | Residential loans held for sale
Assets
Loans held for sale		268	213
Level 2 | Commercial real estate loans held for sale
Assets
Loans held for sale		57	43
Level 3
Assets
Securities available for sale		0	0
Loans held for sale		0	0
Derivative assets		0	0
Money market mutual fund		0	0
Other investments		0	5
Total other investment securities, at fair value		0	5
Total assets		0	5
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		0	0
Level 3 | Commercial real estate loans held for sale
Assets
Loans held for sale		$ 0	$ 0

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