Other Comprehensive Income (Loss) (Reclassifications out of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ (30,944)	$ (30,010)	$ (62,073)	$ (58,147)
Loss on early extinguishment of debt	0	0	(4,735)	0
Income tax (expense) benefit	(33,574)	(32,242)	(64,773)	(64,091)
Investment securities gains, net	0	1,985	67	2,710
Salaries and other personnel expense	(188,611)	(177,806)	(376,844)	(356,713)
Net income available to common shareholders	57,898	53,233	107,870	104,637
Net Unrealized Gains (Losses) on Cash Flow Hedges [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	(64)	(112)	(140)	(224)
Loss on early extinguishment of debt			(197)	0
Income tax (expense) benefit	25	44	130	87
Net income available to common shareholders	(39)	(68)	(207)	(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	0	(764)	(26)	(1,043)
Investment securities gains, net	0	1,985	67	2,710
Net income available to common shareholders	0	1,221	41	1,667
Post-Retirement Unfunded Health Benefit [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense) benefit	(4)	(16)	(40)	(32)
Salaries and other personnel expense	10	42	104	84
Net income available to common shareholders	$ 6	$ 26	$ 64	$ 52