Loans and Allowance for Credit Losses Present Loans, Net of Unearned Income and Their Related Allowance for Loan Losses, by Portfolio Segment (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011	Mar. 31, 2011		Dec. 31, 2010
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	$ 159,190			$ 164,240
Allowance for loan losses measured for impairment under FASB ASC Section 310-10-35	97,306			106,032
Allowance for loan losses	256,496		256,471	270,272		274,271
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	11,656,188			11,347,579
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 310-10-35	301,412			525,629
Loans, net of unearned income	11,957,600		11,968,970	11,873,208
Real-estate commercial mortage [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	50,619			26,327
Allowance for loan losses measured for impairment under FASB ASC Section 310-10-35	31,033			22,231
Allowance for loan losses	81,652		85,112	48,558		40,831
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	4,523,691			4,224,868
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 310-10-35	110,737			167,811
Loans, net of unearned income	4,634,428			4,392,679
Commercial - industrial, financial, and agricultural
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	47,484			36,709
Allowance for loan losses measured for impairment under FASB ASC Section 310-10-35	32,272			63,471
Allowance for loan losses	79,756		74,896	100,180		101,436
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	3,441,018			3,472,225
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 310-10-35	77,210			220,443
Loans, net of unearned income	3,518,228			3,692,668
Real-estate - home equity [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	9,549			5,656
Allowance for loan losses measured for impairment under FASB ASC Section 310-10-35	3,534			0
Allowance for loan losses	13,083		12,841	5,656		6,454
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	1,595,522			1,620,340
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 310-10-35	6,358			0
Loans, net of unearned income	1,601,880			1,620,340
Real-estate - residential mortgage [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	8,045			15,288
Allowance for loan losses measured for impairment under FASB ASC Section 310-10-35	16,806			4,287
Allowance for loan losses	24,851		22,986	19,575		17,425
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	1,136,199			1,003,323
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 310-10-35	40,748			18,928
Loans, net of unearned income	1,176,947			1,022,251
Real-estate - construction
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	17,551			39,448
Allowance for loan losses measured for impairment under FASB ASC Section 310-10-35	13,635			16,043
Allowance for loan losses	31,186		30,066	55,491		58,117
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	581,381			629,359
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 310-10-35	66,319			118,447
Loans, net of unearned income	647,700			747,806
Consumer
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	1,638			4,736
Allowance for loan losses measured for impairment under FASB ASC Section 310-10-35	5			0
Allowance for loan losses	1,643		2,083	4,736		4,669
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	308,487			337,413
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 310-10-35	8			0
Loans, net of unearned income	308,495			337,413
Leasing and other and overdrafts [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	3,253			2,576
Allowance for loan losses measured for impairment under FASB ASC Section 310-10-35	21			0
Allowance for loan losses	3,274		2,397	2,576		3,840
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	69,890			60,051
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 310-10-35	32			0
Loans, net of unearned income	69,922			60,051
Unallocated
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	21,051	[1]		33,500	[1]
Allowance for loan losses	$ 21,051	[1]	$ 26,090	$ 33,500	[1]	$ 41,499

[1] The Corporation’s unallocated allowance, which was approximately 8% and 12% as of March 31, 2012 and 2011, respectively, was reasonable and appropriate as the estimates used in the allocation process are inherently imprecise.