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Investment Securities - Contractual Maturities and Weighted-Average Yields of Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Securities available for sale
Due in 1 year or less	$ 632
Due after 1 year through 5 years	14,150
Due after 5 years through 10 years	7,096
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	78,567
Securities available for sale	100,445	$ 79,213
Amortized cost of securities available for sale
Due in 1 year or less	628
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost	14,091
Due after 5 years through 10 years	6,860
Due > 10 Years	75,990
Amortized Cost	$ 97,569	77,984
Weighted average yield for securities available for sale
Due in 1 Year or Less	1.43%
Due > 1 Year through 5 Years	0.74%
Due > 5 Years through 10 Years	1.76%
Due > 10 Years	2.20%
Total weighted average yield	1.96%
U.S. Treasury securities
Securities available for sale
Due in 1 year or less	$ 202
Due after 1 year through 5 years	9,116
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	9,318	4,124
Amortized cost of securities available for sale
Amortized Cost	9,302	4,122
RMBS, Agency
Securities available for sale
Due in 1 year or less	0
Due after 1 year through 5 years	65
Due after 5 years through 10 years	1,175
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	74,226
Securities available for sale	75,466	62,839
Amortized cost of securities available for sale
Amortized Cost	73,248	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	1,237
Securities available for sale	1,237	1,499
Amortized cost of securities available for sale
Amortized Cost	1,035	1,235
RMBS
Securities available for sale
Due in 1 year or less	0
Due after 1 year through 5 years	65
Due after 5 years through 10 years	1,175
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	75,463
Securities available for sale	76,703	64,338
Amortized cost of securities available for sale
Amortized Cost	$ 74,283	63,238
Weighted average yield for securities available for sale
Weighted-average expected life	4 years
CMBS, Agency
Securities available for sale
Due in 1 year or less	$ 90
Due after 1 year through 5 years	2,896
Due after 5 years through 10 years	5,645
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	3,104
Securities available for sale	11,735	9,426
Amortized cost of securities available for sale
Amortized Cost	$ 11,298	9,303
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	$ 340
Due after 1 year through 5 years	2,073
Due after 5 years through 10 years	276
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	0
Securities available for sale	2,689	1,325
Amortized cost of securities available for sale
Amortized Cost	$ 2,686	$ 1,321

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