Investment Securities - Schedule of Contractual Maturities and Weighted-Average Yields of Securities (Detail) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Securities available for sale
Due in 1 year or less	$ 471
Due after 1 year through 5 years	3,877
Due after 5 years through 10 years	6,001
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	35,819
Securities available for sale	46,168	$ 46,150
Amortized cost of securities available for sale
Due in 1 year or less	471
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost	3,877
Due after 5 years through 10 years	5,992
Due 10 Years	35,532
Amortized Cost	$ 45,872	46,728
Weighted average yield for securities available for sale
Due in 1 Year or Less	1.51%
Due 1 Year through 5 Years	2.45%
Due 5 Years through 10 Years	2.65%
Due 10 Years	3.09%
Total weighted average yield	2.96%
Carrying value of securities held to maturity
Due in 1 year or less	$ 0
Due 1 year through 5 years	59
Due after 5 years through 10 years	914
Due after 10 years	32,921
Carrying Value	33,894	36,771
Fair value of securities held to maturity
Due in 1 Year or Less	0
Due 1 Year through 5 Years	62
Due 5 Years through 10 Years	974
Due 10 Years	34,228
Fair Value	$ 35,264	36,619
Weighted average yield for securities held to maturity
Due 1 Year through 5 Years	3.65%
Due 5 Years through 10 Years	3.12%
Due 10 Years	3.24%
Total weighted average yield	3.24%
U.S. Treasury securities
Securities available for sale
Due in 1 year or less	$ 0
Due after 1 year through 5 years	1,483
Due after 5 years through 10 years	2,672
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	0
Securities available for sale	4,155	6,144
Amortized cost of securities available for sale
Amortized Cost	4,173	6,146
RMBS, Agency
Securities available for sale
Due in 1 year or less	1
Due after 1 year through 5 years	28
Due after 5 years through 10 years	731
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	32,953
Securities available for sale	33,713	31,903
Amortized cost of securities available for sale
Amortized Cost	33,727	32,710
Carrying value of securities held to maturity
Due in 1 year or less	0
Due 1 year through 5 years	0
Due after 5 years through 10 years	85
Due after 10 years	30,024
Carrying Value	30,109	33,061
Fair value of securities held to maturity
Fair Value	31,289	32,977
RMBS, Non-agency
Securities available for sale
Due in 1 year or less	0
Due after 1 year through 5 years	0
Due after 5 years through 10 years	0
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	1,612
Securities available for sale	1,612	1,742
Amortized cost of securities available for sale
Amortized Cost	1,313	1,440
RMBS
Securities available for sale
Due in 1 year or less	1
Due after 1 year through 5 years	28
Due after 5 years through 10 years	731
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	34,565
Securities available for sale	35,325	33,645
Amortized cost of securities available for sale
Amortized Cost	$ 35,040	34,150
Weighted average yield for securities held to maturity
Weighted-average expected life	5 years
CMBS, Agency
Securities available for sale
Due in 1 year or less	$ 11
Due after 1 year through 5 years	1,833
Due after 5 years through 10 years	2,298
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	1,254
Securities available for sale	5,396	4,739
Amortized cost of securities available for sale
Amortized Cost	5,368	4,806
Carrying value of securities held to maturity
Due in 1 year or less	0
Due 1 year through 5 years	59
Due after 5 years through 10 years	829
Due after 10 years	2,897
Carrying Value	3,785	3,710
Fair value of securities held to maturity
Fair Value	$ 3,975	3,642
Weighted average yield for securities held to maturity
Weighted-average expected life	5 years 4 months 24 days
Other securities
Securities available for sale
Due in 1 year or less	$ 459
Due after 1 year through 5 years	533
Due after 5 years through 10 years	300
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	0
Securities available for sale	1,292	1,622
Amortized cost of securities available for sale
Amortized Cost	$ 1,291	$ 1,626

Available-for-sale Securities, Expected Debt Maturities, Amortized Cost Basis, Rolling Maturity

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Available-for-sale Securities, Expected Debt Maturities, Fair Value, Rolling Maturity [Abstract]

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next rolling fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing after rolling tenth fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing after rolling tenth fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next rolling fiscal year through fifth year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Fair value of investment in debt security, measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next rolling fiscal year through fifth year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

Reference 2: 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 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

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Weighted average yield of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), maturing after tenth rolling fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

+ References