Loans - Trouble Debt Restructuring Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	$ 1,245	$ 1,034	$ 1,179	$ 1,048
Trouble debt restructuring interest income recognized	13	8	34	27
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	483	461	487	495
Trouble debt restructuring interest income recognized	5	3	12	11
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	364	330	361	360
Trouble debt restructuring interest income recognized	2	2	6	7
Commercial Loans [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	85	87	92	88
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	34	44	34	47
Trouble debt restructuring interest income recognized	3	1	6	4
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	762	573	692	553
Trouble debt restructuring interest income recognized	8	5	22	16
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	745	550	676	529
Trouble debt restructuring interest income recognized	8	5	22	15
Consumer Loans [Member] | Credit Card Receivables [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	17	23	16	24
Trouble debt restructuring interest income recognized				$ 1