Loans and Allowance for Loan Losses - Loans in Commercial Portfolio Segment Monitored for Credit Quality (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 29,714	$ 28,476
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	28,194	26,469
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	895	1,045
Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	625	962
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	20,934	19,450
Commercial and Industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	20,007	18,594
Commercial and Industrial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	609	466
Commercial and Industrial [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	318	390
Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	677	871
Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	636	674
Construction [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	37	126
Construction [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4	71
Commercial mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,103	8,155
Commercial mortgage [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,551	7,201
Commercial mortgage [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	249	453
Commercial mortgage [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 303	$ 501