Fair Value Measurements - Additional Information Relating To Asset-Backed Securities and Collateralized Debt Obligations (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	$ 526		$ 557
Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	159
Available-for-sale securities backed by collateral	526	[1]
Level 2 [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading collateralized debt obligations and related collateral	64
Level 2 [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	88
Available-for-sale securities backed by collateral	341	[1]
Level 2 [Member] | Commercial Mortgages [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	185	[1]
Level 2 [Member] | Residential, Subprime, Financing Receivable [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	71
Level 3 [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading collateralized debt obligations and related collateral	481
AAA - A Rating [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	296	[1]
AAA - A Rating [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	156
Available-for-sale securities backed by collateral	185	[1]
AAA - A Rating [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	111	[1]
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 collateralized debt obligations and related collateral	64
AAA - A Rating [Member] | Level 2 [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	111	[1]
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	88
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	111	[1]
AAA - A Rating [Member] | Level 2 [Member] | Commercial Mortgages [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	185	[1]
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	185	[1]
AAA - A Rating [Member] | Level 2 [Member] | Residential, Subprime, Financing Receivable [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	68
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 collateralized debt obligations and related collateral	0
CCC - Unrated [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	66	[1]
CCC - Unrated [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	3
Available-for-sale securities backed by collateral	1	[1]
CCC - Unrated [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	65	[1]
CCC - Unrated [Member] | Level 2 [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	66	[1]
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	[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	65	[1]
CCC - Unrated [Member] | Level 2 [Member] | Residential, Subprime, Financing Receivable [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	3
BBB -B Rating [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	164	[1]
BBB -B Rating [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	79	[1]
BBB -B Rating [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	85	[1]
BBB -B Rating [Member] | Level 2 [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading collateralized debt obligations and related collateral	0
BBB -B Rating [Member] | Level 2 [Member] | Trading asset-backed securities and related collateral [Member] | Corporate Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading collateralized debt obligations and related collateral	0
BBB -B Rating [Member] | Level 2 [Member] | Trading asset-backed securities and related collateral [Member] | Other Debt Obligations [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading collateralized debt obligations and related collateral	0
BBB -B Rating [Member] | Level 2 [Member] | Alt [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	164	[1]
BBB -B 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	79	[1]
BBB -B Rating [Member] | Level 2 [Member] | Alt [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	85	[1]
BBB -B Rating [Member] | Level 3 [Member] | Trading asset-backed securities and related collateral [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading collateralized debt obligations and related collateral	481
BBB -B Rating [Member] | Level 3 [Member] | Trading asset-backed securities and related collateral [Member] | Corporate Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading collateralized debt obligations and related collateral	303
BBB -B Rating [Member] | Level 3 [Member] | Trading asset-backed securities and related collateral [Member] | Other Debt Obligations [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading collateralized debt obligations and related collateral	$ 178

[1] We utilize Standard & Poor's ("S&P") as the primary source of credit ratings in the tables above. If S&P ratings are not available, ratings by Moody's and Fitch are used in that order.