Investment Securities - Schedule of Expected Maturities and Weighted Average Yields of Investment Securities by Major Security Type (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Securities available for sale
Due in 1 Year or Less	$ 1,300
Due 1 Year through 5 Years	23,427
Due 5 Years through 10 Years	14,121
Due 10 Years	583
Available-for-sale Securities	39,431	$ 39,508
Amortized cost of securities available for sale
Due in 1 Year or Less	1,303
Due 1 Year through 5 Years	23,143
Due 5 Years through 10 Years	13,787
Due 10 Years	520
Total Amortized Cost	$ 38,753	38,859
Weighted average yield for securities available for sale
Due in 1 Year or Less	1.16%
Due 1 Year through 5 Years	2.06%
Due 5 Years through 10 Years	2.92%
Due 10 Years	6.58%
Total weighted average yield	2.40%
Carrying value of securities held to maturity
Due in 1 Year or Less	$ 14
Due 1 Year through 5 Years	1,602
Due 5 Years through 10 Years	18,489
Due 10 Years	3,606
Carrying Value	23,711	22,500
Fair value of securities held to maturity
Due in 1 Year or Less	15
Due 1 Year through 5 Years	1,649
Due 5 Years through 10 Years	19,459
Due 10 Years	3,790
Fair Value	$ 24,913	23,634
Weighted average yield for securities held to maturity
Due in 1 Year or Less	5.67%
Due 1 Year through 5 Years	2.77%
Due 5 Years through 10 Years	2.50%
Due 10 Years	3.33%
Total weighted average yield	2.64%
U.S. Treasury securities
Carrying value of securities held to maturity
Due in 1 Year or Less	$ 0
Due 1 Year through 5 Years	198
Due 5 Years through 10 Years	0
Due 10 Years	0
Carrying Value	198
Fair value of securities held to maturity
Fair Value	200
U.S. Treasury securities
Securities available for sale
Due in 1 Year or Less	603
Due 1 Year through 5 Years	3,841
Due 5 Years through 10 Years	1
Due 10 Years	0
Available-for-sale Securities	4,445	4,118
Amortized cost of securities available for sale
Total Amortized Cost	4,412	4,114
Corporate debt securities guaranteed by U.S. government agencies
Securities available for sale
Due in 1 Year or Less	0
Due 1 Year through 5 Years	326
Due 5 Years through 10 Years	29
Due 10 Years	0
Available-for-sale Securities	355	800
Amortized cost of securities available for sale
Total Amortized Cost	356	819
RMBS
Securities available for sale
Due in 1 Year or Less	280
Due 1 Year through 5 Years	15,794
Due 5 Years through 10 Years	11,218
Due 10 Years	473
Available-for-sale Securities	27,765	25,381
Amortized cost of securities available for sale
Total Amortized Cost	27,170	24,742
RMBS | Agency
Securities available for sale
Due in 1 Year or Less	272
Due 1 Year through 5 Years	14,756
Due 5 Years through 10 Years	9,583
Due 10 Years	0
Available-for-sale Securities	24,611	21,995
Amortized cost of securities available for sale
Total Amortized Cost	24,409	21,804
Carrying value of securities held to maturity
Due in 1 Year or Less	14
Due 1 Year through 5 Years	1,302
Due 5 Years through 10 Years	16,079
Due 10 Years	3,219
Carrying Value	20,614	20,163
Fair value of securities held to maturity
Fair Value	21,674	21,210
RMBS | Non-Agency
Securities available for sale
Due in 1 Year or Less	8
Due 1 Year through 5 Years	1,038
Due 5 Years through 10 Years	1,635
Due 10 Years	473
Available-for-sale Securities	3,154	3,386
Amortized cost of securities available for sale
Total Amortized Cost	2,761	2,938
CMBS
Securities available for sale
Due in 1 Year or Less	213
Due 1 Year through 5 Years	2,326
Due 5 Years through 10 Years	2,661
Due 10 Years	20
Available-for-sale Securities	5,220	5,519
Amortized cost of securities available for sale
Total Amortized Cost	5,175	5,531
CMBS | Agency
Securities available for sale
Due in 1 Year or Less	80
Due 1 Year through 5 Years	1,829
Due 5 Years through 10 Years	1,517
Due 10 Years	20
Available-for-sale Securities	3,446	3,723
Amortized cost of securities available for sale
Total Amortized Cost	3,431	3,751
Carrying value of securities held to maturity
Due in 1 Year or Less	0
Due 1 Year through 5 Years	102
Due 5 Years through 10 Years	2,410
Due 10 Years	387
Carrying Value	2,899	2,337
Fair value of securities held to maturity
Fair Value	3,039	2,424
CMBS | Non-Agency
Securities available for sale
Due in 1 Year or Less	133
Due 1 Year through 5 Years	497
Due 5 Years through 10 Years	1,144
Due 10 Years	0
Available-for-sale Securities	1,774	1,796
Amortized cost of securities available for sale
Total Amortized Cost	1,744	1,780
Other ABS
Securities available for sale
Due in 1 Year or Less	153
Due 1 Year through 5 Years	1,135
Due 5 Years through 10 Years	195
Due 10 Years	0
Available-for-sale Securities	1,483	2,662
Amortized cost of securities available for sale
Total Amortized Cost	1,478	2,618
Other securities
Securities available for sale
Due in 1 Year or Less	51
Due 1 Year through 5 Years	5
Due 5 Years through 10 Years	17
Due 10 Years	90
Available-for-sale Securities	163	1,028
Amortized cost of securities available for sale
Total Amortized Cost	$ 162	$ 1,035