Other Comprehensive Income (Loss) (Reclassifications out of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ (30,010)	$ (27,162)	$ (58,147)	$ (55,029)
Income tax (expense) benefit	(32,242)	(27,078)	(64,091)	(55,686)
Investment securities gains, net	1,985	0	2,710	1,331
Salaries and other personnel expense	(177,806)	(182,205)	(356,713)	(366,365)
Net income available to common shareholders	53,233	44,313	104,637	90,170
Net Unrealized Gains (Losses) on Cash Flow Hedges [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	(112)	(112)	(224)	(224)
Income tax (expense) benefit	44	44	87	87
Net income available to common shareholders	(68)	(68)	(137)	(137)
Net Unrealized Gains (Losses) on Investment Securities Available for Sale [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense) benefit	(764)	0	(1,043)	(513)
Investment securities gains, net	1,985	0	2,710	1,331
Net income available to common shareholders	1,221	0	1,667	818
Post-Retirement Unfunded Health Benefit [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense) benefit	(16)	(28)	(32)	(56)
Salaries and other personnel expense	42	72	84	144
Net income available to common shareholders	$ 26	$ 44	$ 52	$ 88