FAIR VALUE MEASUREMENTS - Schedule of Fair Value Measurements (Details) - USD ($) $ in Millions		Jun. 30, 2017		Dec. 31, 2016
Assets
Securities available for sale	[1]	$ 19,257		$ 19,501
Loans held for sale, at fair value		520		583
Derivative assets		484	[2],[3]	759
Money market mutual fund		92		91
Other investments		5		5
Total other investment securities, at fair value		97		96
Total assets		20,358		20,939
Liabilities
Total derivative liabilities		403	[2],[3]	778
Total liabilities		403		778
Interest rate swaps
Assets
Derivative assets		341	[3]	609
Liabilities
Total derivative liabilities		277	[3]	645
Foreign exchange contracts
Assets
Derivative assets		132	[3]	134
Liabilities
Total derivative liabilities		121	[3]	126
Other contracts
Assets
Derivative assets		11	[3]	16
Liabilities
Total derivative liabilities		5	[3]	7
Mortgage-backed securities
Assets
Securities available for sale		19,238		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		386		504
Commercial loans held for sale
Assets
Loans held for sale, at fair value		134		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		92		91
Other investments		0		0
Total other investment securities, at fair value		92		91
Total assets		104		121
Liabilities
Total derivative liabilities		0	[3]	0
Total liabilities		0		0
Level 1 | Interest rate swaps
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		19,245		19,471
Loans held for sale, at fair value		520		583
Derivative assets		484	[3]	759
Money market mutual fund		0		0
Other investments		5		5
Total other investment securities, at fair value		5		5
Total assets		20,254		20,818
Liabilities
Total derivative liabilities		403	[3]	778
Total liabilities		403		778
Level 2 | Interest rate swaps
Assets
Derivative assets		341	[3]	609
Liabilities
Total derivative liabilities		277	[3]	645
Level 2 | Foreign exchange contracts
Assets
Derivative assets		132	[3]	134
Liabilities
Total derivative liabilities		121	[3]	126
Level 2 | Other contracts
Assets
Derivative assets		11	[3]	16
Liabilities
Total derivative liabilities		5	[3]	7
Level 2 | Mortgage-backed securities
Assets
Securities available for sale		19,238		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		386		504
Level 2 | Commercial loans held for sale
Assets
Loans held for sale, at fair value		134		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 swaps
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 variation margin payments that are characterized as settlement per the rules of the Company’s central counterparties that became effective January 3, 2017.

[3] Amounts reflect variation margin payments that are characterized as settlement per the rules of the Company’s central counterparties that became effective January 3, 2017.