Fair Value Measurements - Additional Information Relating To Asset-Backed Securities and Collateralized Debt Obligations (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	$ 411	$ 448
Level 2 [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	226
Level 3 [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	258
Estimate of Fair Value Measurement [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	484
AAA - A Rating [Member] | Level 2 [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	191
AAA - A Rating [Member] | Level 2 [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	221
AAA - A Rating [Member] | Level 2 [Member] | Trading asset-backed securities and related collateral [Member] | Student Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	68
AAA - A Rating [Member] | Level 2 [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	91
AAA - A Rating [Member] | Level 2 [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Home Equity Line of Credit [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	95
AAA - A Rating [Member] | Level 2 [Member] | Subprime [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	62
AAA - A Rating [Member] | Level 2 [Member] | Commercial Mortgages [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	96
AAA - A Rating [Member] | Level 3 [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	0
AAA - A Rating [Member] | Level 3 [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	0
AAA - A Rating [Member] | Level 3 [Member] | Trading asset-backed securities and related collateral [Member] | Student Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	0
AAA - A Rating [Member] | Level 3 [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	0
AAA - A Rating [Member] | Level 3 [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Home Equity Line of Credit [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	0
AAA - A Rating [Member] | Level 3 [Member] | Subprime [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	0
AAA - A Rating [Member] | Level 3 [Member] | Commercial Mortgages [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	0
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	191
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	221
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Trading asset-backed securities and related collateral [Member] | Student Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	68
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	91
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Home Equity Line of Credit [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	95
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Subprime [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	62
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Commercial Mortgages [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	96
BBB -B Rating [Member] | Level 2 [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	0
Available-for-sale securities backed by collateral	94
BBB -B Rating [Member] | Level 2 [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Other [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	94
BBB -B Rating [Member] | Level 3 [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	258
Available-for-sale securities backed by collateral	0
BBB -B Rating [Member] | Level 3 [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Other [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	0
BBB -B Rating [Member] | Estimate of Fair Value Measurement [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	258
Available-for-sale securities backed by collateral	94
BBB -B Rating [Member] | Estimate of Fair Value Measurement [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Other [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	94
CCC - Unrated [Member] | Level 2 [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	411
CCC - Unrated [Member] | Level 2 [Member] | Trading asset-backed securities and related collateral [Member] | Other Line Of Credit [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	126
CCC - Unrated [Member] | Level 2 [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	1
CCC - Unrated [Member] | Level 2 [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Home Equity Line of Credit [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	125
CCC - Unrated [Member] | Level 2 [Member] | Subprime [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	5
CCC - Unrated [Member] | Level 3 [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	0
CCC - Unrated [Member] | Level 3 [Member] | Trading asset-backed securities and related collateral [Member] | Other Line Of Credit [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	0
CCC - Unrated [Member] | Level 3 [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	0
CCC - Unrated [Member] | Level 3 [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Home Equity Line of Credit [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	0
CCC - Unrated [Member] | Level 3 [Member] | Subprime [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	0
CCC - Unrated [Member] | Estimate of Fair Value Measurement [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	411
CCC - Unrated [Member] | Estimate of Fair Value Measurement [Member] | Trading asset-backed securities and related collateral [Member] | Other Line Of Credit [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	126
CCC - Unrated [Member] | Estimate of Fair Value Measurement [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	1
CCC - Unrated [Member] | Estimate of Fair Value Measurement [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member] | Home Equity Line of Credit [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	125
CCC - Unrated [Member] | Estimate of Fair Value Measurement [Member] | Subprime [Member] | Trading asset-backed securities and related collateral [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	$ 5