Investment Securities - Schedule of Contractual Maturities and Weighted-Average Yields of Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Securities available for sale
Due in 1 year or less	$ 624
Due after 1 year through 5 years	2,517
Due after 5 years through 10 years	5,711
Due 10 Years	28,803
Available-for-sale Securities	37,655	$ 40,737
Amortized cost of securities available for sale
Due in 1 year or less	624
Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Amortized Cost Basis	2,515
Due after 5 years through 10 years	5,706
Due 10 Years	28,783
Total Amortized Cost	$ 37,628	40,733
Weighted average yield for securities available for sale
Due in 1 Year or Less	1.13%
Due 1 Year through 5 Years	1.88%
Due 5 Years through 10 Years	2.05%
Due 10 Years	2.65%
Total weighted average yield	2.49%
Carrying value of securities held to maturity
Due in 1 year or less	$ 200
Due 1 year through 5 years	987
Due after 5 years through 10 years	359
Due after 10 years	27,438
Carrying Value	28,984	25,712
Fair value of securities held to maturity
Due in 1 Year or Less	200
Due 1 Year through 5 Years	1,031
Due 5 Years through 10 Years	366
Due 10 Years	27,840
Fair Value	$ 29,437	26,196
Weighted average yield for securities held to maturity
Due in 1 Year or Less	1.11%
Due 1 Year through 5 Years	2.37%
Due 5 Years through 10 Years	2.87%
Due 10 Years	2.77%
Total weighted average yield	2.75%
U.S. Treasury securities
Carrying value of securities held to maturity
Due in 1 year or less	$ 200
Due 1 year through 5 years	0
Due after 5 years through 10 years	0
Due after 10 years	0
Carrying Value	200	199
Fair value of securities held to maturity
Fair Value	200	199
U.S. Treasury securities
Securities available for sale
Due in 1 year or less	200
Due after 1 year through 5 years	1,238
Due after 5 years through 10 years	3,733
Due 10 Years	0
Available-for-sale Securities	5,171	5,065
Amortized cost of securities available for sale
Total Amortized Cost	5,168	5,103
RMBS
Securities available for sale
Due in 1 year or less	4
Due after 1 year through 5 years	45
Due after 5 years through 10 years	507
Due 10 Years	27,236
Available-for-sale Securities	27,792	29,249
Amortized cost of securities available for sale
Total Amortized Cost	$ 27,735	29,179
Weighted average yield for securities held to maturity
Weighted-average expected life	5 years 6 days
RMBS \| Agency
Securities available for sale
Due in 1 year or less	$ 4
Due after 1 year through 5 years	45
Due after 5 years through 10 years	507
Due 10 Years	25,122
Available-for-sale Securities	25,678	26,527
Amortized cost of securities available for sale
Total Amortized Cost	26,013	26,830
Carrying value of securities held to maturity
Due in 1 year or less	0
Due 1 year through 5 years	0
Due after 5 years through 10 years	120
Due after 10 years	24,860
Carrying Value	24,980	22,125
Fair value of securities held to maturity
Fair Value	25,395	22,573
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
Due 10 Years	2,114
Available-for-sale Securities	2,114	2,722
Amortized cost of securities available for sale
Total Amortized Cost	$ 1,722	2,349
CMBS
Securities available for sale
Available-for-sale Securities		4,988
Amortized cost of securities available for sale
Total Amortized Cost		5,011
Weighted average yield for securities held to maturity
Weighted-average expected life	4 years 4 months 6 days
CMBS \| Agency
Securities available for sale
Due in 1 year or less	$ 19
Due after 1 year through 5 years	592
Due after 5 years through 10 years	1,123
Due 10 Years	1,441
Available-for-sale Securities	3,175	3,304
Amortized cost of securities available for sale
Total Amortized Cost	3,209	3,335
Carrying value of securities held to maturity
Due in 1 year or less	0
Due 1 year through 5 years	987
Due after 5 years through 10 years	239
Due after 10 years	2,578
Carrying Value	3,804	3,388
Fair value of securities held to maturity
Fair Value	3,842	3,424
CMBS \| Non-Agency
Securities available for sale
Available-for-sale Securities		1,684
Amortized cost of securities available for sale
Total Amortized Cost		1,676
Other ABS
Securities available for sale
Due in 1 year or less	172
Due after 1 year through 5 years	310
Due after 5 years through 10 years	0
Due 10 Years	30
Available-for-sale Securities	512	714
Amortized cost of securities available for sale
Total Amortized Cost	$ 513	714
Weighted average yield for securities held to maturity
Weighted-average expected life	1 year 6 days
Other securities
Securities available for sale
Due in 1 year or less	$ 229
Due after 1 year through 5 years	332
Due after 5 years through 10 years	348
Due 10 Years	96
Available-for-sale Securities	1,005	721
Amortized cost of securities available for sale
Total Amortized Cost	$ 1,003	$ 726

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