Other Comprehensive Income (Loss) (Reclassifications out of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ (30,303)	$ (27,131)	$ (88,450)	$ (82,160)
Income tax (expense) benefit	(36,058)	(25,868)	(100,149)	(81,554)
Investment securities gains, net	0	0	2,710	1,331
Salaries and other personnel expense	(177,907)	(193,749)	(534,621)	(560,115)
Net income available to common shareholders	55,369	44,229	160,006	134,399
Net Unrealized Gains (Losses) on Cash Flow Hedges [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	(112)	(112)	(336)	(336)
Income tax (expense) benefit	43	43	130	130
Net income available to common shareholders	(69)	(69)	(206)	(206)
Net Unrealized Gains (Losses) on Investment Securities Available for Sale [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense) benefit			(1,043)	(513)
Investment securities gains, net			2,710	1,331
Net income available to common shareholders			1,667	818
Post-Retirement Unfunded Health Benefit [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense) benefit	(36)	0	(68)	(56)
Salaries and other personnel expense	94	0	178	144
Net income available to common shareholders	$ 58	$ 0	$ 110	$ 88