SECURITIES - Amortized Cost and Fair Value of Securities Held to Maturity (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Investment Securities Held To Maturity [Line Items]
Amortized Cost	$ 2,966	$ 3,275
Gross Unrealized Gains	106	42
Gross Unrealized Losses	0	(12)
Fair Value	3,072	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	1	0
Gross Unrealized Losses	0	0
Fair Value	161	175
Agency Mortgage-Backed Securities [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	811	949
Gross Unrealized Gains	32	8
Gross Unrealized Losses	0	(2)
Fair Value	843	955
Agency Collateralized Mortgage Obligations [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	571	721
Gross Unrealized Gains	19	5
Gross Unrealized Losses	0	(6)
Fair Value	590	720
Commercial Mortgage-Backed Securities [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	278	308
Gross Unrealized Gains	12	3
Gross Unrealized Losses	0	(2)
Fair Value	290	309
States of the U.S. and Political Subdivisions (municipals) [Member]
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1,144	1,120
Gross Unrealized Gains	42	26
Gross Unrealized Losses	0	(2)
Fair Value	$ 1,186	$ 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
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
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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).

+ References

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-Publisher FASB
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