Loans and Leases and the Allowance for Credit Losses - Recorded Investment in Loans and Leases on Basis of Company's Impairment Methodology (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 63,659,042	$ 66,570,957
Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	930,237	1,065,551
Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	62,371,468	65,058,292
Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	357,337	447,114
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	17,911,149	17,776,953
Commercial, Financial, Leasing, etc. [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	118,513	159,761
Commercial, Financial, Leasing, etc. [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	17,776,379	17,599,755
Commercial, Financial, Leasing, etc. [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	16,257	17,437
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	26,345,267	25,993,790
Commercial Real Estate [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	413,443	480,335
Commercial Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	25,623,585	25,123,758
Commercial Real Estate [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	308,239	389,697
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	9,228,003	11,240,837
Residential Real Estate [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	326,860	349,477
Residential Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	8,870,942	10,854,591
Residential Real Estate [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	30,201	36,769
Consumer loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	10,174,623	11,559,377
Consumer loans [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	71,421	75,978
Consumer loans [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	10,100,562	11,480,188
Consumer loans [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 2,640	$ 3,211