Investment Securities - Investment Securities Held-to-Maturity (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	$ 46,481	$ 46,050
Held-to-maturity securities, Unrealized Gains	326	51
Held-to-maturity securities, Unrealized Losses Other	(169)	(1,137)
Held-to-maturity securities, Fair Value	46,638	44,964
U.S. Treasury and Agencies [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	4,402	5,102
Held-to-maturity securities, Unrealized Gains	35	2
Held-to-maturity securities, Unrealized Losses Other	(7)	(143)
Held-to-maturity securities, Fair Value	4,430	4,961
Residential Mortgage-Backed Securities [Member] \| Agency [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	42,054	40,920
Held-to-maturity securities, Unrealized Gains	289	45
Held-to-maturity securities, Unrealized Losses Other	(162)	(994)
Held-to-maturity securities, Fair Value	42,181	39,971
Asset-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	5
Held-to-maturity securities, Fair Value	7
Asset-Backed Securities [Member] \| Collateralized Loan Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Unrealized Gains	1	1
Held-to-maturity securities, Fair Value	1	1
Asset-Backed Securities [Member] \| Other Asset-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	5	5
Held-to-maturity securities, Unrealized Gains	1	2
Held-to-maturity securities, Fair Value	6	7
Obligations of State and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	4	6
Held-to-maturity securities, Unrealized Gains		1
Held-to-maturity securities, Fair Value	4	7
Obligations of Foreign Governments [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	8	9
Held-to-maturity securities, Fair Value	8	9
Other [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	8	8
Held-to-maturity securities, Fair Value	$ 8	$ 8

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

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)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-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).

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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