Investment Securities - Schedule of Expected Maturities and Weighted Average Yields of Investment Securities by Major Security Type (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Securities available for sale
Due in 1 Year or Less	$ 1,203
Due 1 Year through 5 Years	17,533
Due 5 Years through 10 Years	20,676
Due 10 Years	330
Available-for-sale Securities	39,742	$ 40,737
Amortized cost of securities available for sale
Due in 1 Year or Less	1,204
Due 1 Year through 5 Years	17,346
Due 5 Years through 10 Years	20,598
Due 10 Years	291
Total Amortized Cost	$ 39,439	40,733
Weighted average yield for securities available for sale
Due in 1 Year or Less	1.42%
Due 1 Year through 5 Years	2.51%
Due 5 Years through 10 Years	2.32%
Due 10 Years	6.26%
Total weighted average yield	2.40%
Carrying value of securities held to maturity
Due in 1 Year or Less	$ 221
Due 1 Year through 5 Years	3,736
Due 5 Years through 10 Years	19,049
Due 10 Years	5,644
Carrying Value	28,650	25,712
Fair value of securities held to maturity
Due in 1 Year or Less	220
Due 1 Year through 5 Years	3,832
Due 5 Years through 10 Years	19,513
Due 10 Years	5,762
Fair Value	$ 29,327	26,196
Weighted average yield for securities held to maturity
Due in 1 Year or Less	0.67%
Due 1 Year through 5 Years	2.52%
Due 5 Years through 10 Years	2.67%
Due 10 Years	3.33%
Total weighted average yield	2.76%
U.S. Treasury securities
Carrying value of securities held to maturity
Due in 1 Year or Less	$ 199
Due 1 Year through 5 Years	0
Due 5 Years through 10 Years	0
Due 10 Years	0
Carrying Value	199	199
Fair value of securities held to maturity
Fair Value	199	199
U.S. Treasury securities
Securities available for sale
Due in 1 Year or Less	202
Due 1 Year through 5 Years	647
Due 5 Years through 10 Years	4,290
Due 10 Years	0
Available-for-sale Securities	5,139	5,065
Amortized cost of securities available for sale
Total Amortized Cost	5,110	5,103
RMBS
Securities available for sale
Due in 1 Year or Less	184
Due 1 Year through 5 Years	13,180
Due 5 Years through 10 Years	14,640
Due 10 Years	234
Available-for-sale Securities	28,238	29,249
Amortized cost of securities available for sale
Total Amortized Cost	27,983	29,179
RMBS \| Agency
Securities available for sale
Due in 1 Year or Less	173
Due 1 Year through 5 Years	12,086
Due 5 Years through 10 Years	13,780
Due 10 Years	0
Available-for-sale Securities	26,039	26,527
Amortized cost of securities available for sale
Total Amortized Cost	26,186	26,830
Carrying value of securities held to maturity
Due in 1 Year or Less	22
Due 1 Year through 5 Years	1,781
Due 5 Years through 10 Years	18,421
Due 10 Years	4,571
Carrying Value	24,795	22,125
Fair value of securities held to maturity
Fair Value	25,397	22,573
RMBS \| Non-Agency
Securities available for sale
Due in 1 Year or Less	11
Due 1 Year through 5 Years	1,094
Due 5 Years through 10 Years	860
Due 10 Years	234
Available-for-sale Securities	2,199	2,722
Amortized cost of securities available for sale
Total Amortized Cost	1,797	2,349
CMBS
Securities available for sale
Due in 1 Year or Less	329
Due 1 Year through 5 Years	3,106
Due 5 Years through 10 Years	1,394
Due 10 Years	0
Available-for-sale Securities	4,829	4,988
Amortized cost of securities available for sale
Total Amortized Cost	4,816	5,011
CMBS \| Agency
Securities available for sale
Due in 1 Year or Less	151
Due 1 Year through 5 Years	1,899
Due 5 Years through 10 Years	971
Due 10 Years	0
Available-for-sale Securities	3,021	3,304
Amortized cost of securities available for sale
Total Amortized Cost	3,033	3,335
Carrying value of securities held to maturity
Due in 1 Year or Less	0
Due 1 Year through 5 Years	1,955
Due 5 Years through 10 Years	628
Due 10 Years	1,073
Carrying Value	3,656	3,388
Fair value of securities held to maturity
Fair Value	3,731	3,424
CMBS \| Non-Agency
Securities available for sale
Due in 1 Year or Less	178
Due 1 Year through 5 Years	1,207
Due 5 Years through 10 Years	423
Due 10 Years	0
Available-for-sale Securities	1,808	1,684
Amortized cost of securities available for sale
Total Amortized Cost	1,783	1,676
Other ABS
Securities available for sale
Due in 1 Year or Less	282
Due 1 Year through 5 Years	265
Due 5 Years through 10 Years	0
Due 10 Years	0
Available-for-sale Securities	547	714
Amortized cost of securities available for sale
Total Amortized Cost	546	714
Other securities
Securities available for sale
Due in 1 Year or Less	206
Due 1 Year through 5 Years	335
Due 5 Years through 10 Years	352
Due 10 Years	96
Available-for-sale Securities	989	721
Amortized cost of securities available for sale
Total Amortized Cost	$ 984	$ 726

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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