Loans and leases and the allowance for credit losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Loans And Leases Receivable [Line Items]
Current	$ 63,208,720	$ 63,854,815
30-89 Days past due	749,170	730,901
Purchased impaired	425,232	447,114
Nonaccrual	1,052,794	1,013,176
Total	65,924,267	66,570,957
Non-acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	331,283	358,397
Acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	157,068	166,554
Commercial, Financial, Leasing, etc. [Member]
Loans And Leases Receivable [Line Items]
Current	17,144,615	17,511,052
30-89 Days past due	90,708	62,479
Purchased impaired	16,741	17,437
Nonaccrual	204,199	151,908
Total	17,469,138	17,776,953
Commercial, Financial, Leasing, etc. [Member] | Non-acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	3,669	23,490
Commercial, Financial, Leasing, etc. [Member] | Acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	9,206	10,587
Commercial [Member]
Loans And Leases Receivable [Line Items]
Current	21,513,598	21,759,997
30-89 Days past due	185,101	118,249
Purchased impaired	121,090	132,962
Nonaccrual	186,239	193,859
Total	22,058,740	22,273,173
Commercial [Member] | Non-acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	11,444	13,111
Commercial [Member] | Acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	41,268	54,995
Residential Builder and Developer [Member]
Loans And Leases Receivable [Line Items]
Current	781,748	757,311
30-89 Days past due	30,019	35,419
Purchased impaired	167,207	187,764
Nonaccrual	166,796	181,865
Total	1,166,648	1,189,526
Residential Builder and Developer [Member] | Non-acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	513	3,258
Residential Builder and Developer [Member] | Acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	20,365	23,909
Other Commercial Construction [Member]
Loans And Leases Receivable [Line Items]
Current	2,541,578	2,379,953
30-89 Days past due	42,849	35,274
Purchased impaired	78,254	68,971
Nonaccrual	40,170	36,812
Total	2,719,431	2,531,091
Other Commercial Construction [Member] | Non-acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	2,279	509
Other Commercial Construction [Member] | Acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	14,301	9,572
Residential [Member]
Loans And Leases Receivable [Line Items]
Current	9,742,192	9,811,956
30-89 Days past due	279,879	337,969
Purchased impaired	38,709	36,769
Nonaccrual	252,799	249,314
Total	10,665,995	10,794,316
Residential [Member] | Non-acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	309,366	313,184
Residential [Member] | Acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	43,050	45,124
Residential Alt-A [Member]
Loans And Leases Receivable [Line Items]
Current	315,500	331,021
30-89 Days past due	24,779	19,692
Purchased impaired
Nonaccrual	88,303	95,808
Total	428,582	446,521
Residential Alt-A [Member] | Non-acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing
Residential Alt-A [Member] | Acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing
Home Equity Lines and Loans [Member]
Loans And Leases Receivable [Line Items]
Current	6,068,137	6,199,591
30-89 Days past due	33,433	40,759
Purchased impaired	3,231	3,211
Nonaccrual	72,021	58,071
Total	6,204,181	6,321,950
Home Equity Lines and Loans [Member] | Non-acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing
Home Equity Lines and Loans [Member] | Acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	27,359	20,318
Automobile [Member]
Loans And Leases Receivable [Line Items]
Current	2,466,577	2,442,502
30-89 Days past due	30,363	40,461
Purchased impaired
Nonaccrual	20,095	25,107
Total	2,517,193	2,508,321
Automobile [Member] | Non-acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing
Automobile [Member] | Acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	158	251
Other [Member]
Loans And Leases Receivable [Line Items]
Current	2,634,775	2,661,432
30-89 Days past due	32,039	40,599
Purchased impaired
Nonaccrual	22,172	20,432
Total	2,694,359	2,729,106
Other [Member] | Non-acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	4,012	4,845
Other [Member] | Acquired [Member]
Loans And Leases Receivable [Line Items]
90 Days or more past due and accruing	$ 1,361	$ 1,798