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Investment Securities - Contractual Maturities and Weighted-Average Yields of Securities (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Securities available for sale
Due in 1 year or less	$ 503
Due after 1 year through 5 years	3,822
Due after 5 years through 10 years	7,380
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	67,508
Securities available for sale	79,213	$ 46,150
Amortized cost of securities available for sale
Due in 1 year or less	503
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost	3,816
Due after 5 years through 10 years	7,334
Due 10 Years	66,331
Amortized Cost	$ 77,984	46,728
Weighted average yield for securities available for sale
Due in 1 Year or Less	1.43%
Due 1 Year through 5 Years	2.37%
Due 5 Years through 10 Years	2.60%
Due 10 Years	3.06%
Total weighted average yield	2.97%
U.S. Treasury securities
Securities available for sale
Due in 1 year or less	$ 0
Due after 1 year through 5 years	1,476
Due after 5 years through 10 years	2,648
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	0
Securities available for sale	4,124	6,144
Amortized cost of securities available for sale
Amortized Cost	4,122	6,146
RMBS, Agency
Securities available for sale
Due in 1 year or less	0
Due after 1 year through 5 years	36
Due after 5 years through 10 years	891
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	61,912
Securities available for sale	62,839	31,903
Amortized cost of securities available for sale
Amortized Cost	62,003	32,710
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	1,499
Securities available for sale	1,499	1,742
Amortized cost of securities available for sale
Amortized Cost	1,235	1,440
RMBS
Securities available for sale
Due in 1 year or less	0
Due after 1 year through 5 years	36
Due after 5 years through 10 years	891
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	63,411
Securities available for sale	64,338	33,645
Amortized cost of securities available for sale
Amortized Cost	$ 63,238	34,150
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	$ 2
Due after 1 year through 5 years	1,753
Due after 5 years through 10 years	3,574
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	4,097
Securities available for sale	9,426	4,739
Amortized cost of securities available for sale
Amortized Cost	$ 9,303	4,806
Weighted average yield for securities available for sale
Weighted-average expected life	5 years 5 months
Other securities
Securities available for sale
Due in 1 year or less	$ 501
Due after 1 year through 5 years	557
Due after 5 years through 10 years	267
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	0
Securities available for sale	1,325	1,622
Amortized cost of securities available for sale
Amortized Cost	$ 1,321	$ 1,626

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