Investment Securities - Schedule of Expected Maturities and Weighted Average Yields of Investment Securities by Major Security Type (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Securities available for sale
Due in 1 Year or Less	$ 1,519
Due 1 Year through 5 Years	16,678
Due 5 Years through 10 Years	22,131
Due 10 Years	409
Available-for-sale Securities	40,737	$ 39,061
Amortized cost of securities available for sale
Due in 1 Year or Less	1,521
Due 1 Year through 5 Years	16,548
Due 5 Years through 10 Years	22,286
Due 10 Years	378
Total Amortized Cost	$ 40,733	38,804
Weighted average yield for securities available for sale
Due in 1 Year or Less	1.26%
Due 1 Year through 5 Years	2.17%
Due 5 Years through 10 Years	2.51%
Due 10 Years	6.55%
Total weighted average yield	2.36%
Carrying value of securities held to maturity
Due in 1 Year or Less	$ 0
Due 1 Year through 5 Years	1,692
Due 5 Years through 10 Years	18,874
Due 10 Years	5,146
Carrying Value	25,712	24,619
Fair value of securities held to maturity
Due in 1 Year or Less	0
Due 1 Year through 5 Years	1,714
Due 5 Years through 10 Years	19,314
Due 10 Years	5,168
Fair Value	$ 26,196	25,317
Weighted average yield for securities held to maturity
Due in 1 Year or Less	0.00%
Due 1 Year through 5 Years	2.71%
Due 5 Years through 10 Years	2.54%
Due 10 Years	3.33%
Total weighted average yield	2.70%
U.S. Treasury securities
Carrying value of securities held to maturity
Due in 1 Year or Less	$ 0
Due 1 Year through 5 Years	199
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	198
U.S. Treasury securities
Securities available for sale
Due in 1 Year or Less	652
Due 1 Year through 5 Years	2,854
Due 5 Years through 10 Years	1,559
Due 10 Years	0
Available-for-sale Securities	5,065	4,660
Amortized cost of securities available for sale
Total Amortized Cost	5,103	4,664
RMBS
Securities available for sale
Due in 1 Year or Less	123
Due 1 Year through 5 Years	10,696
Due 5 Years through 10 Years	18,114
Due 10 Years	316
Available-for-sale Securities	29,249	27,311
Amortized cost of securities available for sale
Total Amortized Cost	29,179	27,012
RMBS \| Agency
Securities available for sale
Due in 1 Year or Less	94
Due 1 Year through 5 Years	9,755
Due 5 Years through 10 Years	16,678
Due 10 Years	0
Available-for-sale Securities	26,527	24,285
Amortized cost of securities available for sale
Total Amortized Cost	26,830	24,332
Carrying value of securities held to maturity
Due in 1 Year or Less	0
Due 1 Year through 5 Years	1,363
Due 5 Years through 10 Years	16,418
Due 10 Years	4,344
Carrying Value	22,125	21,513
Fair value of securities held to maturity
Fair Value	22,573	22,133
RMBS \| Non-Agency
Securities available for sale
Due in 1 Year or Less	29
Due 1 Year through 5 Years	941
Due 5 Years through 10 Years	1,436
Due 10 Years	316
Available-for-sale Securities	2,722	3,026
Amortized cost of securities available for sale
Total Amortized Cost	2,349	2,680
CMBS
Securities available for sale
Due in 1 Year or Less	290
Due 1 Year through 5 Years	2,324
Due 5 Years through 10 Years	2,374
Due 10 Years	0
Available-for-sale Securities	4,988	5,379
Amortized cost of securities available for sale
Total Amortized Cost	5,011	5,413
CMBS \| Agency
Securities available for sale
Due in 1 Year or Less	144
Due 1 Year through 5 Years	1,544
Due 5 Years through 10 Years	1,616
Due 10 Years	0
Available-for-sale Securities	3,304	3,664
Amortized cost of securities available for sale
Total Amortized Cost	3,335	3,690
Carrying value of securities held to maturity
Due in 1 Year or Less	0
Due 1 Year through 5 Years	130
Due 5 Years through 10 Years	2,456
Due 10 Years	802
Carrying Value	3,388	2,907
Fair value of securities held to maturity
Fair Value	3,424	2,986
CMBS \| Non-Agency
Securities available for sale
Due in 1 Year or Less	146
Due 1 Year through 5 Years	780
Due 5 Years through 10 Years	758
Due 10 Years	0
Available-for-sale Securities	1,684	1,715
Amortized cost of securities available for sale
Total Amortized Cost	1,676	1,723
Other ABS
Securities available for sale
Due in 1 Year or Less	247
Due 1 Year through 5 Years	460
Due 5 Years through 10 Years	7
Due 10 Years	0
Available-for-sale Securities	714	1,340
Amortized cost of securities available for sale
Total Amortized Cost	714	1,345
Other securities
Securities available for sale
Due in 1 Year or Less	207
Due 1 Year through 5 Years	344
Due 5 Years through 10 Years	77
Due 10 Years	93
Available-for-sale Securities	721	371
Amortized cost of securities available for sale
Total Amortized Cost	$ 726	$ 370

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