FAIR VALUE MEASUREMENTS - Schedule of Fair Value Measurements (Details) - USD ($) $ in Millions		Sep. 30, 2017		Dec. 31, 2016
Assets
Securities available for sale	[1]	$ 19,982		$ 19,501
Loans held for sale, at fair value		500		583
Derivative assets		664	[2],[3]	759
Money market mutual fund		160		91
Other investments		5		5
Total other investment securities, at fair value		165		96
Total assets		21,311		20,939
Liabilities
Total derivative liabilities		485	[2],[3]	778
Total liabilities		485		778
Interest rate contracts
Assets
Derivative assets		508	[3]	609
Liabilities
Total derivative liabilities		338	[3]	645
Foreign exchange contracts
Assets
Derivative assets		146	[3]	134
Liabilities
Total derivative liabilities		142	[3]	126
Other contracts
Assets
Derivative assets		10	[3]	16
Liabilities
Total derivative liabilities		5	[3]	7
Mortgage-backed securities
Assets
Securities available for sale		19,963		19,446
State and political subdivisions
Assets
Securities available for sale		7		8
Equity securities
Assets
Securities available for sale				17
U.S. Treasury and other
Assets
Securities available for sale		12		30
Residential loans held for sale
Assets
Loans held for sale, at fair value		349		504
Commercial loans held for sale
Assets
Loans held for sale, at fair value		151		79
Level 1
Assets
Securities available for sale		12		30
Loans held for sale, at fair value		0		0
Derivative assets		0	[3]	0
Money market mutual fund		160		91
Other investments		0		0
Total other investment securities, at fair value		160		91
Total assets		172		121
Liabilities
Total derivative liabilities		0	[3]	0
Total liabilities		0		0
Level 1 | Interest rate contracts
Assets
Derivative assets		0	[3]	0
Liabilities
Total derivative liabilities		0	[3]	0
Level 1 | Foreign exchange contracts
Assets
Derivative assets		0	[3]	0
Liabilities
Total derivative liabilities		0	[3]	0
Level 1 | Other contracts
Assets
Derivative assets		0	[3]	0
Liabilities
Total derivative liabilities		0	[3]	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
Level 1 | U.S. Treasury and other
Assets
Securities available for sale		12		30
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		19,970		19,471
Loans held for sale, at fair value		500		583
Derivative assets		664	[3]	759
Money market mutual fund		0		0
Other investments		5		5
Total other investment securities, at fair value		5		5
Total assets		21,139		20,818
Liabilities
Total derivative liabilities		485	[3]	778
Total liabilities		485		778
Level 2 | Interest rate contracts
Assets
Derivative assets		508	[3]	609
Liabilities
Total derivative liabilities		338	[3]	645
Level 2 | Foreign exchange contracts
Assets
Derivative assets		146	[3]	134
Liabilities
Total derivative liabilities		142	[3]	126
Level 2 | Other contracts
Assets
Derivative assets		10	[3]	16
Liabilities
Total derivative liabilities		5	[3]	7
Level 2 | Mortgage-backed securities
Assets
Securities available for sale		19,963		19,446
Level 2 | State and political subdivisions
Assets
Securities available for sale		7		8
Level 2 | Equity securities
Assets
Securities available for sale				17
Level 2 | U.S. Treasury and other
Assets
Securities available for sale		0		0
Level 2 | Residential loans held for sale
Assets
Loans held for sale, at fair value		349		504
Level 2 | Commercial loans held for sale
Assets
Loans held for sale, at fair value		151		79
Level 3
Assets
Securities available for sale		0		0
Loans held for sale, at fair value		0		0
Derivative assets		0	[3]	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	[3]	0
Total liabilities		0		0
Level 3 | Interest rate contracts
Assets
Derivative assets		0	[3]	0
Liabilities
Total derivative liabilities		0	[3]	0
Level 3 | Foreign exchange contracts
Assets
Derivative assets		0	[3]	0
Liabilities
Total derivative liabilities		0	[3]	0
Level 3 | Other contracts
Assets
Derivative assets		0	[3]	0
Liabilities
Total derivative liabilities		0	[3]	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
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.

[2] Amounts reflect changes in the treatment of variation margin on certain centrally cleared derivatives.

[3] Amounts reflect changes in the treatment of variation margin on certain centrally cleared derivatives.