Investment Securities - Contractual Maturities and Weighted-Average Yields of Securities (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2021	Dec. 31, 2020
Securities available for sale
Due in 1 year or less	$ 2,098
Due after 1 year through 5 years	13,153
Due after 5 years through 10 years	6,540
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	79,975
Securities available for sale	101,766	$ 100,445
Amortized cost of securities available for sale
Due in 1 year or less	2,096
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost	13,087
Due after 5 years through 10 years	6,376
Due > 10 Years	78,777
Amortized Cost	$ 100,336	97,569
Weighted average yield for securities available for sale
Due in 1 Year or Less	0.66%
Due > 1 Year through 5 Years	0.53%
Due > 5 Years through 10 Years	1.51%
Due > 10 Years	1.77%
Total weighted average yield	1.57%
U.S. Treasury securities
Securities available for sale
Due in 1 year or less	$ 1,401
Due after 1 year through 5 years	7,830
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	9,231	9,318
Amortized cost of securities available for sale
Amortized Cost	9,211	9,302
RMBS, Agency
Securities available for sale
Due in 1 year or less	0
Due after 1 year through 5 years	97
Due after 5 years through 10 years	1,139
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	75,970
Securities available for sale	77,206	75,466
Amortized cost of securities available for sale
Amortized Cost	76,318	73,248
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	1,116
Securities available for sale	1,116	1,237
Amortized cost of securities available for sale
Amortized Cost	908	1,035
RMBS
Securities available for sale
Due in 1 year or less	0
Due after 1 year through 5 years	97
Due after 5 years through 10 years	1,139
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	77,086
Securities available for sale	78,322	76,703
Amortized cost of securities available for sale
Amortized Cost	$ 77,226	74,283
Weighted average yield for securities available for sale
Weighted-average expected life	5 years 4 months 24 days
CMBS, Agency
Securities available for sale
Due in 1 year or less	$ 399
Due after 1 year through 5 years	2,666
Due after 5 years through 10 years	5,133
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	2,889
Securities available for sale	11,087	11,735
Amortized cost of securities available for sale
Amortized Cost	$ 10,781	11,298
Weighted average yield for securities available for sale
Weighted-average expected life	5 years 7 months 6 days
Other securities
Securities available for sale
Due in 1 year or less	$ 298
Due after 1 year through 5 years	2,560
Due after 5 years through 10 years	268
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	0
Securities available for sale	3,126	2,689
Amortized cost of securities available for sale
Amortized Cost	$ 3,118	$ 2,686

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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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