Loans and leases and the allowance for credit losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Loans And Leases Receivable [Line Items]
Current	$ 61,514,824	$ 57,167,794
30-89 Days past due	673,055	725,654
Purchased impaired	528,001	653,362
Nonaccrual	925,231	1,097,581
Loans and leases, net of unearned discount	64,111,955	60,096,005
Commercial, financial, leasing, etc [Member]
Loans And Leases Receivable [Line Items]
Current	16,496,862	15,493,803
30-89 Days past due	50,980	37,112
Purchased impaired	17,434	23,762
Nonaccrual	121,806	163,598
Loans and leases, net of unearned discount	16,704,575	15,734,436
Commercial [Member]
Loans And Leases Receivable [Line Items]
Current	20,926,702	19,658,761
30-89 Days past due	142,780	172,641
Purchased impaired	151,685	192,804
Nonaccrual	172,246	171,111
Loans and leases, net of unearned discount	21,460,221	20,259,448
Residential builder and developer [Member]
Loans And Leases Receivable [Line Items]
Current	781,007	845,680
30-89 Days past due	26,920	49,353
Purchased impaired	244,017	297,005
Nonaccrual	225,529	281,576
Loans and leases, net of unearned discount	1,306,352	1,508,333
Other commercial construction [Member]
Loans And Leases Receivable [Line Items]
Current	2,056,594	2,393,304
30-89 Days past due	36,738	41,049
Purchased impaired	69,337	78,105
Nonaccrual	26,709	106,325
Loans and leases, net of unearned discount	2,203,843	2,643,333
Residential [Member]
Loans And Leases Receivable [Line Items]
Current	9,534,751	6,626,182
30-89 Days past due	270,560	256,017
Purchased impaired	41,297	56,741
Nonaccrual	182,217	172,681
Loans and leases, net of unearned discount	10,346,716	7,400,075
Residential Alt-A [Member]
Loans And Leases Receivable [Line Items]
Current	340,568	383,834
30-89 Days past due	25,203	34,077
Nonaccrual	95,733	105,179
Loans and leases, net of unearned discount	461,504	523,090
Home equity lines and loans [Member]
Loans And Leases Receivable [Line Items]
Current	6,300,811	6,570,675
30-89 Days past due	44,791	43,516
Purchased impaired	4,231	4,635
Nonaccrual	56,300	47,150
Loans and leases, net of unearned discount	6,423,932	6,681,385
Automobile [Member]
Loans And Leases Receivable [Line Items]
Current	2,429,579	2,644,330
30-89 Days past due	40,813	48,342
Nonaccrual	25,537	26,835
Loans and leases, net of unearned discount	2,496,274	2,720,108
Other [Member]
Loans And Leases Receivable [Line Items]
Current	2,647,950	2,551,225
30-89 Days past due	34,270	43,547
Purchased impaired		310
Nonaccrual	19,154	23,126
Loans and leases, net of unearned discount	2,708,538	2,625,797
Non-Acquired [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	309,420	287,876
Non-Acquired [Member] | Commercial, financial, leasing, etc [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	2,574	7,601
Non-Acquired [Member] | Commercial [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	12,479	9,983
Non-Acquired [Member] | Residential builder and developer [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	5,009	13,603
Non-Acquired [Member] | Other commercial construction [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	8,077	968
Non-Acquired [Member] | Residential [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	276,314	250,472
Non-Acquired [Member] | Other [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	4,967	5,249
Acquired [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	161,424	163,738
Acquired [Member] | Commercial, financial, leasing, etc [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	14,919	8,560
Acquired [Member] | Commercial [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	54,329	54,148
Acquired [Member] | Residential builder and developer [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	23,870	21,116
Acquired [Member] | Other commercial construction [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	6,388	23,582
Acquired [Member] | Residential [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	41,577	37,982
Acquired [Member] | Home equity lines and loans [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	17,799	15,409
Acquired [Member] | Automobile [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	345	601
Acquired [Member] | Other [Member]
Loans And Leases Receivable [Line Items]
90 days or more past due and accruing	$ 2,197	$ 2,340