Investment Securities - Contractual Maturities and Weighted-Average Yields of Securities (Detail) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Securities available for sale
Due in 1 year or less	$ 404
Due after 1 year through 5 years	13,965
Due after 5 years through 10 years	6,596
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	78,888
Securities available for sale	99,853	$ 79,213
Amortized cost of securities available for sale
Due in 1 year or less	402
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost	13,901
Due after 5 years through 10 years	6,334
Due > 10 Years	76,098
Amortized Cost	$ 96,735	77,984
Weighted average yield for securities available for sale
Due in 1 Year or Less	1.44%
Due > 1 Year through 5 Years	0.82%
Due > 5 Years through 10 Years	1.93%
Due > 10 Years	2.37%
Total weighted average yield	2.11%
U.S. Treasury securities
Securities available for sale
Due in 1 year or less	$ 101
Due after 1 year through 5 years	9,244
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	0
Securities available for sale	9,345	4,124
Amortized cost of securities available for sale
Amortized Cost	9,331	4,122
RMBS, Agency
Securities available for sale
Due in 1 year or less	0
Due after 1 year through 5 years	73
Due after 5 years through 10 years	1,073
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	74,220
Securities available for sale	75,366	62,839
Amortized cost of securities available for sale
Amortized Cost	72,948	62,003
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	1,293
Securities available for sale	1,293	1,499
Amortized cost of securities available for sale
Amortized Cost	1,093	1,235
RMBS
Securities available for sale
Due in 1 year or less	0
Due after 1 year through 5 years	73
Due after 5 years through 10 years	1,073
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	75,513
Securities available for sale	76,659	64,338
Amortized cost of securities available for sale
Amortized Cost	$ 74,041	63,238
Weighted average yield for securities available for sale
Weighted-average expected life	3 years 8 months 12 days
CMBS, Agency
Securities available for sale
Due in 1 year or less	$ 52
Due after 1 year through 5 years	2,766
Due after 5 years through 10 years	5,242
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	3,375
Securities available for sale	11,435	9,426
Amortized cost of securities available for sale
Amortized Cost	$ 10,953	9,303
Weighted average yield for securities available for sale
Weighted-average expected life	5 years 3 months 18 days
Other securities
Securities available for sale
Due in 1 year or less	$ 251
Due after 1 year through 5 years	1,882
Due after 5 years through 10 years	281
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	0
Securities available for sale	2,414	1,325
Amortized cost of securities available for sale
Amortized Cost	$ 2,410	$ 1,321

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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 in second through fifth 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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