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	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 89,313,002	$ 90,853,416
Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	761,732	760,452
Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	87,998,335	89,514,932
Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	552,935	578,032
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	22,295,376	22,610,047
Commercial, Financial, Leasing, etc. [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	269,547	268,877
Commercial, Financial, Leasing, etc. [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	22,024,004	22,340,529
Commercial, Financial, Leasing, etc. [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,825	641
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	33,071,654	33,506,394
Commercial Real Estate [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	224,033	224,630
Commercial Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	32,794,553	33,222,080
Commercial Real Estate [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	53,068	59,684
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,724,491	22,590,912
Residential Real Estate [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	202,411	201,479
Residential Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,024,038	21,871,726
Residential Real Estate [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	498,042	517,707
Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	12,221,481	12,146,063
Consumer Loans [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	65,741	65,466
Consumer Loans [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 12,155,740	$ 12,080,597