Allowance for Credit Losses - Recorded Investment in Loans and Leases on Basis of Company's Impairment Methodology (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 87,489,499	$ 66,668,956
Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	779,673	760,124
Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	85,941,497	65,711,095
Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	768,329	197,737
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	20,422,338	19,461,292
Commercial, Financial, Leasing, etc. [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	272,227	206,318
Commercial, Financial, Leasing, etc. [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	20,148,209	19,244,674
Commercial, Financial, Leasing, etc. [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,902	10,300
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	29,197,311	27,567,569
Commercial Real Estate [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	234,132	252,347
Commercial Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	28,863,130	27,148,382
Commercial Real Estate [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	100,049	166,840
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	26,270,103	8,657,301
Residential Real Estate [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	207,949	232,398
Residential Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	25,398,037	8,406,680
Residential Real Estate [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	664,117	18,223
Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	11,599,747	10,982,794
Consumer Loans [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	65,365	69,061
Consumer Loans [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	11,532,121	10,911,359
Consumer Loans [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 2,261	$ 2,374