Loans and Allowance for Credit Losses Past Due Loan Status and Non-Accrual Loans by Portfolio Segment (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
31-59 Days Past Due	$ 50,789	$ 59,634
60-89 Days Past Due	25,584	31,223
>90 Days Past Due and Accruing	29,325	26,221
Non-accrual	179,334	184,832
Total >90 Days	208,659	211,053
Total Past Due	285,032	301,910
Current	12,092,256	11,845,061
Total	12,377,288	12,146,971	11,960,004
Real-estate commercial mortage [Member]
31-59 Days Past Due	11,023	12,993
60-89 Days Past Due	7,514	8,473
>90 Days Past Due and Accruing	3,651	2,160
Non-accrual	55,154	54,960
Total >90 Days	58,805	57,120
Total Past Due	77,342	78,586
Current	4,652,588	4,585,840
Total	4,729,930	4,664,426
Commercial - industrial, financial, and agricultural
31-59 Days Past Due	7,597	8,474
60-89 Days Past Due	5,160	8,042
>90 Days Past Due and Accruing	3,414	1,259
Non-accrual	57,699	65,695
Total >90 Days	61,113	66,954
Total Past Due	73,870	83,470
Current	3,584,613	3,528,595
Total	3,658,483	3,612,065
Commercial - Secured [Member]
31-59 Days Past Due	6,366	8,013
60-89 Days Past Due	4,392	8,030
>90 Days Past Due and Accruing	3,082	1,060
Non-accrual	56,429	63,602
Total >90 Days	59,511	64,662
Total Past Due	70,269	80,705
Current	3,395,965	3,332,739
Total	3,466,234	3,413,444
Commercial - unsecured [Member]
31-59 Days Past Due	1,231	461
60-89 Days Past Due	768	12
>90 Days Past Due and Accruing	332	199
Non-accrual	1,270	2,093
Total >90 Days	1,602	2,292
Total Past Due	3,601	2,765
Current	188,648	195,856
Total	192,249	198,621
Real-estate - home equity [Member]
31-59 Days Past Due	8,116	9,579
60-89 Days Past Due	3,512	3,066
>90 Days Past Due and Accruing	5,136	5,579
Non-accrual	12,332	11,625
Total >90 Days	17,468	17,204
Total Past Due	29,096	29,849
Current	1,660,350	1,602,541
Total	1,689,446	1,632,390
Real-estate - residential mortgage [Member]
31-59 Days Past Due	18,884	21,827
60-89 Days Past Due	8,053	10,296
>90 Days Past Due and Accruing	13,978	13,333
Non-accrual	22,383	21,103
Total >90 Days	36,361	34,436
Total Past Due	63,298	66,559
Current	1,240,156	1,190,873
Total	1,303,454	1,257,432
Real-estate - construction
31-59 Days Past Due	1,036	1,331
60-89 Days Past Due	0	0
>90 Days Past Due and Accruing	204	579
Non-accrual	31,715	31,426
Total >90 Days	31,919	32,005
Total Past Due	32,955	33,336
Current	564,642	550,782
Total	597,597	584,118
Construction - commercial residential [Member]
31-59 Days Past Due	461	466
60-89 Days Past Due	0	0
>90 Days Past Due and Accruing	132	251
Non-accrual	23,787	22,815
Total >90 Days	23,919	23,066
Total Past Due	24,380	23,532
Current	263,585	265,020
Total	287,965	288,552
Construction - Commercial [Member]
31-59 Days Past Due	0	0
60-89 Days Past Due	0	0
>90 Days Past Due and Accruing	72	0
Non-accrual	7,438	8,035
Total >90 Days	7,510	8,035
Total Past Due	7,510	8,035
Current	239,148	218,315
Total	246,658	226,350
Construction other [Member]
31-59 Days Past Due	575	865
60-89 Days Past Due	0	0
>90 Days Past Due and Accruing	0	328
Non-accrual	490	576
Total >90 Days	490	904
Total Past Due	1,065	1,769
Current	61,909	67,447
Total	62,974	69,216
Total Consumer
31-59 Days Past Due	3,419	4,768
60-89 Days Past Due	1,215	1,297
>90 Days Past Due and Accruing	2,776	3,302
Non-accrual	6	13
Total >90 Days	2,782	3,315
Total Past Due	7,416	9,380
Current	301,722	300,484
Total	309,138	309,864
Consumer - direct [Member]
31-59 Days Past Due	2,150	2,842
60-89 Days Past Due	998	953
>90 Days Past Due and Accruing	2,618	3,157
Non-accrual	6	13
Total >90 Days	2,624	3,170
Total Past Due	5,772	6,965
Current	163,059	159,616
Total	168,831	166,581
Consumer - Indirect [Member]
31-59 Days Past Due	1,269	1,926
60-89 Days Past Due	217	344
>90 Days Past Due and Accruing	158	145
Non-accrual	0	0
Total >90 Days	158	145
Total Past Due	1,644	2,415
Current	138,663	140,868
Total	140,307	143,283
Leasing and other and overdrafts [Member]
31-59 Days Past Due	714	662
60-89 Days Past Due	130	49
>90 Days Past Due and Accruing	166	9
Non-accrual	45	10
Total >90 Days	211	19
Total Past Due	1,055	730
Current	88,185	85,946
Total	$ 89,240	$ 86,676