Investment Securities - Schedule of Contractual Maturities and Weighted-Average Yields of Securities (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Securities available for sale
Due in 1 year or less	$ 712
Due after 1 year through 5 years	3,036
Due after 5 years through 10 years	6,817
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	35,323
Securities available for sale	45,888	$ 46,150
Amortized cost of securities available for sale
Due in 1 year or less	713
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost	3,053
Due after 5 years through 10 years	6,814
Due 10 Years	35,502
Amortized Cost	$ 46,082	46,728
Weighted average yield for securities available for sale
Due in 1 Year or Less	1.57%
Due 1 Year through 5 Years	2.46%
Due 5 Years through 10 Years	2.71%
Due 10 Years	3.30%
Total weighted average yield	3.13%
Carrying value of securities held to maturity
Due in 1 year or less	$ 0
Due 1 year through 5 years	68
Due after 5 years through 10 years	765
Due after 10 years	35,670
Carrying Value	36,503	36,771
Fair value of securities held to maturity
Due in 1 Year or Less	0
Due 1 Year through 5 Years	70
Due 5 Years through 10 Years	773
Due 10 Years	36,112
Fair Value	$ 36,955	36,619
Weighted average yield for securities held to maturity
Due 1 Year through 5 Years	3.55%
Due 5 Years through 10 Years	3.16%
Due 10 Years	3.37%
Total weighted average yield	3.36%
U.S. Treasury securities
Securities available for sale
Due in 1 year or less	$ 448
Due after 1 year through 5 years	294
Due after 5 years through 10 years	3,385
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	0
Securities available for sale	4,127	6,144
Amortized cost of securities available for sale
Amortized Cost	4,136	6,146
RMBS, Agency
Securities available for sale
Due in 1 year or less	7
Due after 1 year through 5 years	21
Due after 5 years through 10 years	780
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	32,337
Securities available for sale	33,145	31,903
Amortized cost of securities available for sale
Amortized Cost	33,621	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	89
Due after 10 years	32,579
Carrying Value	32,668	33,061
Fair value of securities held to maturity
Fair Value	33,107	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	1,720
Securities available for sale	1,720	1,742
Amortized cost of securities available for sale
Amortized Cost	1,404	1,440
RMBS
Securities available for sale
Due in 1 year or less	7
Due after 1 year through 5 years	21
Due after 5 years through 10 years	780
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	34,057
Securities available for sale	34,865	33,645
Amortized cost of securities available for sale
Amortized Cost	$ 35,025	34,150
Weighted average yield for securities held to maturity
Weighted-average expected life	5 years 10 months 24 days
CMBS, Agency
Securities available for sale
Due in 1 year or less	$ 10
Due after 1 year through 5 years	1,684
Due after 5 years through 10 years	2,380
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	1,248
Securities available for sale	5,322	4,739
Amortized cost of securities available for sale
Amortized Cost	5,346	4,806
Carrying value of securities held to maturity
Due in 1 year or less	0
Due 1 year through 5 years	68
Due after 5 years through 10 years	676
Due after 10 years	3,091
Carrying Value	3,835	3,710
Fair value of securities held to maturity
Fair Value	3,848	3,642
Other securities
Securities available for sale
Due in 1 year or less	247
Due after 1 year through 5 years	1,037
Due after 5 years through 10 years	272
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	18
Securities available for sale	1,574	1,622
Amortized cost of securities available for sale
Amortized Cost	$ 1,575	$ 1,626
CMBS
Weighted average yield for securities held to maturity
Weighted-average expected life	5 years 7 months 6 days

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=82897076&loc=d3e27161-111563

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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 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 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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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 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&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 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&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