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SECURITIES - Amortized Cost and Fair Value of Securities Held to Maturity (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Investment Securities Held To Maturity [Line Items]
Amortized Cost	$ 3,079	$ 3,254
Gross Unrealized Gains	32	5
Gross Unrealized Losses	(18)	(104)
Fair Value	3,093	3,155
U.S. Treasury [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1	1
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	1	1
US Government Agencies [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	2	2
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	2	2
U.S. Government-Sponsored Entities [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	190	215
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(4)
Fair Value	189	211
Agency Mortgage-Backed Securities [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	952	1,036
Gross Unrealized Gains	4	0
Gross Unrealized Losses	(4)	(26)
Fair Value	952	1,010
Agency Collateralized Mortgage Obligations [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	728	794
Gross Unrealized Gains	6	1
Gross Unrealized Losses	(8)	(24)
Fair Value	726	771
Commercial Mortgage-Backed Securities [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	100	126
Gross Unrealized Gains	4	1
Gross Unrealized Losses	0	(1)
Fair Value	104	126
States of the U.S. and Political Subdivisions [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1,106	1,080
Gross Unrealized Gains	18	3
Gross Unrealized Losses	(5)	(49)
Fair Value	$ 1,119	$ 1,034

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Investment Securities Held To Maturity [Line Items]

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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