FAIR VALUE MEASUREMENTS - Schedule of Fair Value Measurements (Details) - USD ($) $ in Millions		Mar. 31, 2017		Dec. 31, 2016
Assets
Securities available for sale	[1]	$ 19,964		$ 19,501
Loans held for sale, at fair value		448		583
Derivative assets		456	[2]	759
Money market mutual fund		96		91
Other investments		5		5
Total other investment securities, at fair value		101		96
Total assets		20,969		20,939
Liabilities
Total derivative liabilities		425	[2]	778
Total liabilities		425		778
Interest rate swaps
Assets
Derivative assets		350		609
Liabilities
Total derivative liabilities		332		645
Foreign exchange contracts
Assets
Derivative assets		95		134
Liabilities
Total derivative liabilities		85		126
Other contracts
Assets
Derivative assets		11		16
Liabilities
Total derivative liabilities		8		7
Mortgage-backed securities
Assets
Securities available for sale		19,942		19,446
State and political subdivisions
Assets
Securities available for sale		7		8
Equity securities
Assets
Securities available for sale		0		17
U.S. Treasury and other
Assets
Securities available for sale		15		30
Residential loans held for sale
Assets
Loans held for sale, at fair value		365		504
Commercial loans held for sale
Assets
Loans held for sale, at fair value		83		79
Level 1
Assets
Securities available for sale		15		30
Loans held for sale, at fair value		0		0
Derivative assets		0		0
Money market mutual fund		96		91
Other investments		0		0
Total other investment securities, at fair value		96		91
Total assets		111		121
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		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		19,949		19,471
Loans held for sale, at fair value		448		583
Derivative assets		456		759
Money market mutual fund		0		0
Other investments		5		5
Total other investment securities, at fair value		5		5
Total assets		20,858		20,818
Liabilities
Total derivative liabilities		425		778
Total liabilities		425		778
Level 2 | Interest rate swaps
Assets
Derivative assets		350		609
Liabilities
Total derivative liabilities		332		645
Level 2 | Foreign exchange contracts
Assets
Derivative assets		95		134
Liabilities
Total derivative liabilities		85		126
Level 2 | Other contracts
Assets
Derivative assets		11		16
Liabilities
Total derivative liabilities		8		7
Level 2 | Mortgage-backed securities
Assets
Securities available for sale		19,942		19,446
Level 2 | State and political subdivisions
Assets
Securities available for sale		7		8
Level 2 | Equity securities
Assets
Securities available for sale		0		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		365		504
Level 2 | Commercial loans held for sale
Assets
Loans held for sale, at fair value		83		79
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.

[2] Amounts reflect variation margin payments that are characterized as settlement per the rules of the Company’s central counterparties effective for the quarter ended March 31, 2017.