Statement of Comprehensive Income Statement of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net Income, Pretax	$ 81,732	$ 90,974	$ 245,362	$ 253,761
Net Income, Tax	22,720	27,076	72,627	76,889
Net Income, After Tax	59,012	63,898	172,735	176,872
Changes in unrealized securities' holding gains/(losses), before Tax	25,691	(16,207)	31,166	24,293
Changes in unrealized securities' holding gains/(losses), Tax	8,991	(5,672)	10,908	8,503
Changes in unrealized securities' holding gains/(losses), Net of Tax	16,700	(10,535)	20,258	15,790
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity, before Tax	(1,266)	(563)	(2,345)	(1,551)
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity, Tax	(442)	(197)	(821)	(543)
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity , Net of Tax	(824)	(366)	(1,524)	(1,008)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, before Tax	(41)	(14)	(962)	(150)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, Tax	(14)	(5)	(336)	(53)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, Net of Tax	(27)	(9)	(626)	(97)
Net change in unrealized gains/(losses) on securities available for sale, before Tax	24,384	(16,784)	27,859	22,592
Net change in unrealized gains/(losses) on securities available for sale, Tax	8,535	(5,874)	9,751	7,907
Net change in unrealized gains/(losses) on securities available for sale, Net of Tax	15,849	(10,910)	18,108	14,685
Amortization of actuarial losses/(gains), before Tax	1,138	768	3,414	2,398
Amortization of actuarial losses/(gains), Tax	399	269	1,195	839
Amortization of actuarial losses/(gains), Net of Tax	739	499	2,219	1,559
Amortization of prior service cost reclassified to other noninterest expense, before Tax	(410)	(516)	(1,230)	(1,614)
Amortization of prior service cost reclassified to other noninterest expense, Tax	(144)	(181)	(431)	(565)
Amortization of prior service cost reclassified to other noninterest expense, Net of Tax	(266)	(335)	(799)	(1,049)
Net change from defined benefit pension plans, before Tax	1,548	1,284	4,644	4,012
Net change from defined benefit pension plans, Tax	543	450	1,626	1,404
Net change from defined benefit pension plans, Net of Tax	1,005	834	3,018	2,608
Total other comprehensive gains/(losses), before Tax	25,932	(15,500)	32,503	26,604
Total other comprehensive gains/(losses), Tax	9,078	(5,424)	11,377	9,311
Total other comprehensive gains/(losses), Net of Tax	16,854	(10,076)	21,126	17,293
Comprehensive Income, before Tax, Portion Attributable to Parent	107,664	75,474	277,865	280,365
Comprehensive Income, Tax, Portion Attributable to Parent	31,798	21,652	84,004	86,200
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	75,866	53,822	193,861	194,165
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax	0	0	0	0
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Tax	0	0	0	0
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Net of Tax	$ 0	$ 0	$ 0	$ 0