Investment Securities - Schedule of Expected Maturities and Weighted Average Yields of Investment Securities by Major Security Type (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Securities available for sale
Due in 1 Year or Less	$ 2,001
Due 1 Year through 5 Years	21,779
Due 5 Years through 10 Years	15,109
Due 10 Years	619
Securities available for sale	39,508us-gaap_AvailableForSaleSecurities	41,800us-gaap_AvailableForSaleSecurities
Amortized cost of securities available for sale
Due in 1 Year or Less	2,004
Due 1 Year through 5 Years	21,571
Due 5 Years through 10 Years	14,745
Due 10 Years	539
Total Amortized Cost	38,859	41,632
Weighted average yield for securities available for sale
Due in 1 Year or Less	1.23%
Due 1 Year through 5 Years	2.21%
Due 5 Years through 10 Years	3.20%
Due 10 Years	10.61%
Total weighted average yield	2.64%
Carrying value of securities held to maturity
Due in 1 Year or Less	23
Due 1 Year through 5 Years	1,617
Due 5 Years through 10 Years	18,774
Due 10 Years	2,086
Carrying Value	22,500us-gaap_HeldToMaturitySecurities	19,132us-gaap_HeldToMaturitySecurities
Fair value of securities held to maturity
Due in 1 Year or Less	23
Due 1 Year through 5 Years	1,642
Due 5 Years through 10 Years	19,673
Due 10 Years	2,296
Fair Value	23,634	19,185
Weighted average yield for securities held to maturity
Due in 1 Year or Less	4.13%
Due 1 Year through 5 Years	2.73%
Due 5 Years through 10 Years	2.68%
Due 10 Years	3.53%
Total weighted average yield	2.76%
U.S. Treasury and agency debt obligations
Securities available for sale
Due in 1 Year or Less	201
Due 1 Year through 5 Years	3,917
Due 5 Years through 10 Years	0
Due 10 Years	0
Securities available for sale	4,118	834
Amortized cost of securities available for sale
Total Amortized Cost	4,114	832
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	415
Due 5 Years through 10 Years	371
Due 10 Years	14
Securities available for sale	800	1,234
Amortized cost of securities available for sale
Total Amortized Cost	819	1,282
RMBS
Securities available for sale
Due in 1 Year or Less	287
Due 1 Year through 5 Years	13,014
Due 5 Years through 10 Years	11,618
Due 10 Years	462
Securities available for sale	25,381	25,079
Amortized cost of securities available for sale
Total Amortized Cost	24,742	24,737
RMBS \| Agency
Securities available for sale
Due in 1 Year or Less	275
Due 1 Year through 5 Years	12,050
Due 5 Years through 10 Years	9,670
Due 10 Years	0
Securities available for sale	21,995	21,479
Amortized cost of securities available for sale
Total Amortized Cost	21,804	21,572
Carrying value of securities held to maturity
Due in 1 Year or Less	23
Due 1 Year through 5 Years	810
Due 5 Years through 10 Years	17,262
Due 10 Years	2,068
Carrying Value	20,163	17,443
Fair value of securities held to maturity
Fair Value	21,210	17,485
RMBS \| Non-Agency
Securities available for sale
Due in 1 Year or Less	12
Due 1 Year through 5 Years	964
Due 5 Years through 10 Years	1,948
Due 10 Years	462
Securities available for sale	3,386	3,600
Amortized cost of securities available for sale
Total Amortized Cost	2,938	3,165
CMBS
Securities available for sale
Due in 1 Year or Less	461
Due 1 Year through 5 Years	2,803
Due 5 Years through 10 Years	2,235
Due 10 Years	20
Securities available for sale	5,519	6,006
Amortized cost of securities available for sale
Total Amortized Cost	5,531	6,116
CMBS \| Agency
Securities available for sale
Due in 1 Year or Less	337
Due 1 Year through 5 Years	2,335
Due 5 Years through 10 Years	1,051
Due 10 Years	0
Securities available for sale	3,723	4,198
Amortized cost of securities available for sale
Total Amortized Cost	3,751	4,262
Carrying value of securities held to maturity
Due in 1 Year or Less	0
Due 1 Year through 5 Years	807
Due 5 Years through 10 Years	1,512
Due 10 Years	18
Carrying Value	2,337	1,689
Fair value of securities held to maturity
Fair Value	2,424	1,700
CMBS \| Non-Agency
Securities available for sale
Due in 1 Year or Less	124
Due 1 Year through 5 Years	468
Due 5 Years through 10 Years	1,184
Due 10 Years	20
Securities available for sale	1,796	1,808
Amortized cost of securities available for sale
Total Amortized Cost	1,780	1,854
Other ABS
Securities available for sale
Due in 1 Year or Less	954
Due 1 Year through 5 Years	1,386
Due 5 Years through 10 Years	287
Due 10 Years	35
Securities available for sale	2,662	7,136
Amortized cost of securities available for sale
Total Amortized Cost	2,618	7,123
Other securities
Securities available for sale
Due in 1 Year or Less	98
Due 1 Year through 5 Years	244
Due 5 Years through 10 Years	598
Due 10 Years	88
Securities available for sale	1,028	1,511
Amortized cost of securities available for sale
Total Amortized Cost	$ 1,035	$ 1,542

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Available-for-sale Securities, Expected Debt Maturities, Rolling after Year Ten, Amortized Cost Basis

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Available-for-sale Securities, Expected Debt Maturities, Rolling after Year Ten, Weighted Average Yield

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Available-for-sale Securities, Expected Debt Maturities, Rolling Year Six Through Ten, Amortized Cost Basis

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Available-for-sale Securities, Expected Debt Maturities, Rolling Year Six Through Ten, Fair Value

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Available-for-sale Securities, Expected Debt Maturities, Rolling Year Six Through Ten, Weighted Average Yield

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Available-for-sale Securities, Expected Debt Maturities, Rolling Year Two Through Five, Amortized Cost Basis

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Available-for-sale Securities, Expected Debt Maturities, Rolling Year Two Through Five, Fair Value

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Available-for-sale Securities, Expected Debt Maturities, Rolling Year Two Through Five, Weighted Average Yield

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Available-for-sale Securities, Weighted Average Yield

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Held-to-maturity Securities, Expected Debt Maturities, after Five Through Ten Years, Net Carrying Amount

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Held-to-maturity Securities, Expected Debt Maturities, after One Through Five Years, Net Carrying Amount

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Held-to-maturity Securities, Expected Debt Maturities, after Ten Years, Net Carrying Amount

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Held-to-maturity Securities, Expected Debt Maturities, Next Rolling Twelve Months, Fair Value

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Held-to-maturity Securities, Expected Debt Maturities, Rolling after Ten Years, Fair Value

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Held-to-maturity Securities, Expected Debt Maturities, Rolling after Ten Years, Weighted-Average Yield

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Held-to-maturity Securities, Expected Debt Maturities, Rolling Year Six Through Ten, Fair Value

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Held-to-maturity Securities, Expected Debt Maturities, Rolling Year Six Through Ten, Weighted-Average Yield

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Held-to-maturity Securities, Expected Debt Maturities, Rolling Year Two Through Five, Fair Value

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Held-to-maturity Securities, Expected Debt Maturities, Rolling Year Two Through Five, Weighted-Average Yield

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Held to maturity securities expected debt maturities weighted average yield

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Held-to-maturity Securities, Expected Debt Maturities, within One Year, Net Carrying Amount

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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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Fair value of investments in debt securities classified as held-to-maturity.

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