FAIR VALUE MEASUREMENTS - Assets and Liabilities on Recurring Basis (Detail) - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		$ 3,262	$ 3,341
Loans held for sale	[1]	45	14
Derivative assets		207	43
Derivative liabilities		30	39
US Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		159	187
U.S. Government-Sponsored Entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		245	313
Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		1,188	1,161
Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		316	228
States of the U.S. and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		14	21
Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		2	2
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Derivative assets		0	0
Derivative liabilities		0	0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		3,262	3,341
Derivative assets		204	42
Derivative liabilities		30	39
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Derivative assets		3	1
Derivative liabilities		0	0
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		3,262	3,341
Loans held for sale		45	14
Derivative assets		207	43
Assets measured at fair value on a recurring basis, Total		3,514	3,398
Derivative liabilities		30	39
Liabilities measured at fair value on a recurring basis, Total		30	39
Fair Value, Recurring [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		29	36
Fair Value, Recurring [Member] | Not for Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		1	3
Fair Value, Recurring [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		201	43
Fair Value, Recurring [Member] | Non Trading Account Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		6
Fair Value, Recurring [Member] | US Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		159	187
Fair Value, Recurring [Member] | U.S. Government-Sponsored Entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		245	313
Fair Value, Recurring [Member] | Agency Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		1,338	1,429
Fair Value, Recurring [Member] | Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		1,188	1,161
Fair Value, Recurring [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		316	228
Fair Value, Recurring [Member] | States of the U.S. and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		14	21
Fair Value, Recurring [Member] | Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		2	2
Fair Value, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Loans held for sale		0	0
Derivative assets		0	0
Assets measured at fair value on a recurring basis, Total		0	0
Derivative liabilities		0	0
Liabilities measured at fair value on a recurring basis, Total		0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Not for Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Non Trading Account Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		0
Fair Value, Recurring [Member] | Level 1 [Member] | US Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Fair Value, Recurring [Member] | Level 1 [Member] | U.S. Government-Sponsored Entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Agency Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Fair Value, Recurring [Member] | Level 1 [Member] | States of the U.S. and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Fair Value, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		3,262	3,341
Loans held for sale		45	14
Derivative assets		204	42
Assets measured at fair value on a recurring basis, Total		3,511	3,397
Derivative liabilities		30	39
Liabilities measured at fair value on a recurring basis, Total		30	39
Fair Value, Recurring [Member] | Level 2 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		29	36
Fair Value, Recurring [Member] | Level 2 [Member] | Not for Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		1	3
Fair Value, Recurring [Member] | Level 2 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		201	42
Fair Value, Recurring [Member] | Level 2 [Member] | Non Trading Account Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		3
Fair Value, Recurring [Member] | Level 2 [Member] | US Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		159	187
Fair Value, Recurring [Member] | Level 2 [Member] | U.S. Government-Sponsored Entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		245	313
Fair Value, Recurring [Member] | Level 2 [Member] | Agency Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		1,338	1,429
Fair Value, Recurring [Member] | Level 2 [Member] | Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		1,188	1,161
Fair Value, Recurring [Member] | Level 2 [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		316	228
Fair Value, Recurring [Member] | Level 2 [Member] | States of the U.S. and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		14	21
Fair Value, Recurring [Member] | Level 2 [Member] | Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		2	2
Fair Value, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Loans held for sale		0	0
Derivative assets		3	1
Assets measured at fair value on a recurring basis, Total		3	1
Derivative liabilities		0	0
Liabilities measured at fair value on a recurring basis, Total		0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Not for Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		0	1
Fair Value, Recurring [Member] | Level 3 [Member] | Non Trading Account Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		3
Fair Value, Recurring [Member] | Level 3 [Member] | US Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Fair Value, Recurring [Member] | Level 3 [Member] | U.S. Government-Sponsored Entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Agency Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Fair Value, Recurring [Member] | Level 3 [Member] | States of the U.S. and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities available for sale		$ 0	$ 0

[1] Amount represents loans for which we have elected the fair value option. See Note 17.