Investment Securities - Contractual Maturities and Weighted-Average Yields of Securities (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Securities available for sale
Due in 1 year or less	$ 6,025
Due after 1 year through 5 years	9,117
Due after 5 years through 10 years	5,893
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	77,114
Securities available for sale	98,149	$ 100,445
Amortized cost of securities available for sale
Due in 1 year or less	6,019
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost	9,062
Due after 5 years through 10 years	5,761
Due > 10 Years	76,147
Amortized Cost	$ 96,989
Weighted average yield for securities available for sale
Due in 1 Year or Less	0.31%
Due > 1 Year through 5 Years	0.72%
Due > 5 Years through 10 Years	1.66%
Due > 10 Years	1.71%
Total weighted average yield	1.53%
U.S. Treasury securities
Securities available for sale
Due in 1 year or less	$ 5,203
Due after 1 year through 5 years	3,906
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	9,109	9,318
RMBS, Agency
Securities available for sale
Due in 1 year or less	0
Due after 1 year through 5 years	137
Due after 5 years through 10 years	1,106
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	73,389
Securities available for sale	74,632	75,466
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	1,049
Securities available for sale	1,049	1,237
RMBS
Securities available for sale
Due in 1 year or less	0
Due after 1 year through 5 years	137
Due after 5 years through 10 years	1,106
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	74,438
Securities available for sale	$ 75,681	76,703
Weighted average yield for securities available for sale
Weighted-average expected life	5 years 3 months 18 days
CMBS, Agency
Securities available for sale
Due in 1 year or less	$ 570
Due after 1 year through 5 years	2,489
Due after 5 years through 10 years	4,462
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	2,676
Securities available for sale	$ 10,197	11,735
Weighted average yield for securities available for sale
Weighted-average expected life	5 years 6 months
Other securities
Securities available for sale
Due in 1 year or less	$ 252
Due after 1 year through 5 years	2,585
Due after 5 years through 10 years	325
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	0
Securities available for sale	$ 3,162	$ 2,689

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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Debt Maturities, Available-for-Sale, Weighted Average Expected Life

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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
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-SubTopic 30
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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 rolling sixth through 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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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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