Allowance for Credit Losses - Recorded Investment in Loans and Leases on Basis of Company's Impairment Methodology (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 90,853,416	$ 87,489,499
Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	760,452	779,673
Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	89,514,932	85,941,497
Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	578,032	768,329
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	22,610,047	20,422,338
Commercial, Financial, Leasing, etc. [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	268,877	272,227
Commercial, Financial, Leasing, etc. [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	22,340,529	20,148,209
Commercial, Financial, Leasing, etc. [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	641	1,902
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	33,506,394	29,197,311
Commercial Real Estate [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	224,630	234,132
Commercial Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	33,222,080	28,863,130
Commercial Real Estate [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	59,684	100,049
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	22,590,912	26,270,103
Residential Real Estate [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	201,479	207,949
Residential Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,871,726	25,398,037
Residential Real Estate [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	517,707	664,117
Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	12,146,063	11,599,747
Consumer Loans [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	65,466	65,365
Consumer Loans [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 12,080,597	11,532,121
Consumer Loans [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount		$ 2,261