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	Sep. 30, 2012		Jun. 30, 2012	Dec. 31, 2011	Sep. 30, 2011		Jun. 30, 2011	Dec. 31, 2010
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	$ 151,824				$ 163,638
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	82,040				103,340
Allowance for loan losses	233,864		235,736	256,471	266,978		266,683	274,271
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	11,661,818				11,572,789
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	271,183				322,866
Loans, net of unearned income	11,933,001			11,968,970	11,895,655
Real-estate commercial mortage [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	46,889				47,914
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	25,280				33,269
Allowance for loan losses	72,169		69,868	85,112	81,183		73,598	40,831
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	4,539,370				4,377,383
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	93,139				113,772
Loans, net of unearned income	4,632,509				4,491,155
Commercial - industrial, financial, and agricultural
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	44,169				51,510
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	23,705				28,627
Allowance for loan losses	67,874		71,931	74,896	80,137		82,613	101,436
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	3,430,724				3,603,914
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	77,122				86,250
Loans, net of unearned income	3,507,846				3,690,164
Real-estate - home equity [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	10,120				9,843
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	5,316				0
Allowance for loan losses	15,436		14,444	12,841	9,843		9,560	6,454
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	1,594,553				1,630,880
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	8,903				0
Loans, net of unearned income	1,603,456				1,630,880
Real-estate - residential mortgage [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	8,306				7,142
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	20,550				26,194
Allowance for loan losses	28,856		26,711	22,986	33,336		31,912	17,425
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	1,165,013				975,463
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	48,818				66,000
Loans, net of unearned income	1,213,831				1,041,463
Real-estate - construction
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	14,957				20,480
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	7,171				12,565
Allowance for loan losses	22,128		25,559	30,066	33,045		30,570	58,117
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	554,185				596,581
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	43,173				51,817
Loans, net of unearned income	597,358				648,398
Consumer
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	1,858				1,773
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	5				2,629
Allowance for loan losses	1,863		1,816	2,083	4,402		1,755	4,669
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	301,175				322,113
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	7				4,941
Loans, net of unearned income	301,182				327,054
Leasing and other and overdrafts [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	2,980				2,205
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	13				56
Allowance for loan losses	2,993		3,243	2,397	2,261		1,787	3,840
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	76,798				66,455
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	21				86
Loans, net of unearned income	76,819				66,541
Unallocated
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	22,545	[1]			22,771	[1]
Allowance for loan losses	$ 22,545	[1]	$ 22,164	$ 26,090	$ 22,771	[1]	$ 34,888	$ 41,499

[1] The Corporation’s unallocated allowance, which was approximately 10% and 9% as of September 30, 2012 and September 30, 2011, respectively, was, in the opinion of the Corporation's management, reasonable and appropriate given that the estimates used in the allocation process are inherently imprecise.