SECURITIES - Amortized Cost and Fair Value of Securities Held to Maturity (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Investment Securities Held To Maturity [Line Items]
Amortized Cost	$ 3,179	$ 3,275
Gross Unrealized Gains	89	42
Gross Unrealized Losses	(4)	(12)
Fair Value	3,264	3,305
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	1	1
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	1	1
U.S. Government-Sponsored Entities [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	160	175
Gross Unrealized Gains	2	0
Gross Unrealized Losses	0	0
Fair Value	162	175
Agency Mortgage-Backed Securities [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	959	949
Gross Unrealized Gains	33	8
Gross Unrealized Losses	0	(2)
Fair Value	992	955
Agency Collateralized Mortgage Obligations [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	682	721
Gross Unrealized Gains	22	5
Gross Unrealized Losses	0	(6)
Fair Value	704	720
Commercial Mortgage-Backed Securities [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	268	308
Gross Unrealized Gains	3	3
Gross Unrealized Losses	(3)	(2)
Fair Value	268	309
States of the U.S. and Political Subdivisions (municipals) [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1,108	1,120
Gross Unrealized Gains	29	26
Gross Unrealized Losses	(1)	(2)
Fair Value	$ 1,136	$ 1,144

Investment Securities Held To Maturity [Line Items]

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
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-Publisher FASB
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

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- Definition

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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- Definition

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

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-Topic 320
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-Section 50
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