Securities - Amortized Cost and Fair Value of Securities Available-for-Sale and Held-to-Maturity (Detail) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	$ 60,666,000,000	$ 51,791,000,000
Unrealized Gain, Available-for-sale securities	2,056,000,000	1,840,000,000
Unrealized Losses, Available-for-sale securities	(190,000,000)	(350,000,000)
Fair Value, Available-for-sale securities	62,532,000,000	53,281,000,000
Amortized Cost, Held-to-maturity securities	1,741,000,000	2,035,000,000
Unrealized Gain, Held-to-maturity securities	236,000,000	264,000,000
Unrealized Losses, Held-to-maturity securities		(1,000,000)
Fair Value, Held-to-maturity securities	1,977,000,000	2,298,000,000
Foreign debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	5,488,000,000	6,640,000,000
Unrealized Gain, Available-for-sale securities	17,000,000	27,000,000
Unrealized Losses, Available-for-sale securities	(57,000,000)	(97,000,000)
Fair Value, Available-for-sale securities	5,448,000,000	6,570,000,000
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	167,000,000	130,000,000
Unrealized Gain, Available-for-sale securities	8,000,000	10,000,000
Fair Value, Available-for-sale securities	175,000,000	140,000,000
Mortgage-backed securities, U.S. Government agency issued or guaranteed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	15,289,000,000	15,357,000,000
Unrealized Gain, Available-for-sale securities	871,000,000	728,000,000
Unrealized Losses, Available-for-sale securities	(4,000,000)	(3,000,000)
Fair Value, Available-for-sale securities	16,156,000,000	16,082,000,000
Amortized Cost, Held-to-maturity securities	68,000,000	79,000,000
Unrealized Gain, Held-to-maturity securities	13,000,000	13,000,000
Fair Value, Held-to-maturity securities	81,000,000	92,000,000
Mortgage-backed securities, U.S. Government sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	168,000,000	40,000,000
Unrealized Gain, Available-for-sale securities	2,000,000	1,000,000
Fair Value, Available-for-sale securities	170,000,000	41,000,000
Amortized Cost, Held-to-maturity securities	1,212,000,000	1,421,000,000
Unrealized Gain, Held-to-maturity securities	167,000,000	195,000,000
Fair Value, Held-to-maturity securities	1,379,000,000	1,616,000,000
Collateralized mortgage obligations, U.S. Government agency issued or guaranteed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	3,875,000,000	6,881,000,000
Unrealized Gain, Available-for-sale securities	175,000,000	177,000,000
Unrealized Losses, Available-for-sale securities		(3,000,000)
Fair Value, Available-for-sale securities	4,050,000,000	7,055,000,000
Amortized Cost, Held-to-maturity securities	289,000,000	308,000,000
Unrealized Gain, Held-to-maturity securities	46,000,000	44,000,000
Fair Value, Held-to-maturity securities	335,000,000	352,000,000
Obligations of U.S. states and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	775,000,000	566,000,000
Unrealized Gain, Available-for-sale securities	40,000,000	35,000,000
Unrealized Losses, Available-for-sale securities		(1,000,000)
Fair Value, Available-for-sale securities	815,000,000	600,000,000
Amortized Cost, Held-to-maturity securities	44,000,000	61,000,000
Unrealized Gain, Held-to-maturity securities	3,000,000	3,000,000
Fair Value, Held-to-maturity securities	47,000,000	64,000,000
Residential mortgage backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	2,000,000	6,000,000
Unrealized Losses, Available-for-sale securities		(1,000,000)
Fair Value, Available-for-sale securities	2,000,000	5,000,000
Amortized Cost, Held-to-maturity securities	128,000,000	166,000,000
Unrealized Gain, Held-to-maturity securities	7,000,000	9,000,000
Unrealized Losses, Held-to-maturity securities		(1,000,000)
Fair Value, Held-to-maturity securities	135,000,000	174,000,000
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	30,612,000,000	18,199,000,000
Unrealized Gain, Available-for-sale securities	557,000,000	498,000,000
Unrealized Losses, Available-for-sale securities	(30,000,000)	(121,000,000)
Fair Value, Available-for-sale securities	31,139,000,000	18,576,000,000
Direct agency obligations, U.S. Government sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	3,568,000,000	2,501,000,000
Unrealized Gain, Available-for-sale securities	376,000,000	352,000,000
Unrealized Losses, Available-for-sale securities	(2,000,000)
Fair Value, Available-for-sale securities	3,942,000,000	2,853,000,000
Direct agency obligations, U.S. Government agency issued or guaranteed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	1,000,000	2,000,000
Fair Value, Available-for-sale securities	1,000,000	2,000,000
Commercial mortgages backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	257,000,000	444,000,000
Unrealized Gain, Available-for-sale securities	7,000,000	9,000,000
Unrealized Losses, Available-for-sale securities		(2,000,000)
Fair Value, Available-for-sale securities	264,000,000	451,000,000
Home equity backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	322,000,000	369,000,000
Unrealized Losses, Available-for-sale securities	(80,000,000)	(99,000,000)
Fair Value, Available-for-sale securities	242,000,000	270,000,000
Other securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	102,000,000	102,000,000
Unrealized Losses, Available-for-sale securities	(17,000,000)	(22,000,000)
Fair Value, Available-for-sale securities	85,000,000	80,000,000
Corporate and other domestic debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	40,000,000	541,000,000
Unrealized Gain, Available-for-sale securities	3,000,000	3,000,000
Fair Value, Available-for-sale securities	43,000,000	544,000,000
Student loans backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities		13,000,000
Unrealized Losses, Available-for-sale securities		(1,000,000)
Fair Value, Available-for-sale securities		$ 12,000,000

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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- Definition

As of the balance sheet date, the excess of fair value over carrying value (amortized cost) of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding gain.

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- Definition

As of the balance sheet date, the excess of carrying value (amortized cost) over fair value of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding loss.

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