Securities (Narrative) (Detail) (USD $)	3 Months Ended	6 Months Ended
Jun. 30, 2012 Security	Jun. 30, 2011	Jun. 30, 2012 Security	Jun. 30, 2011	Dec. 31, 2011 Security
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale	$ 27,232,000,000		$ 27,232,000,000		$ 24,471,000,000
Securities pledged to secure public funds, trust deposits and borrowing arrangements	14,000,000,000		14,000,000,000		14,300,000,000
Securities in unrealized loss position number	410		410		524
Credit related impairment charge	2,000,000		2,000,000
Total net gains associated with trading account securities	(1,000,000)	10,000,000	29,000,000	31,000,000
Morgan Keegan [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale					2,000,000
Total net gains associated with trading account securities	$ 0	$ 10,000,000	$ 25,000,000	$ 25,000,000

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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Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the available-for-sale investments determined to be temporarily impaired.

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