Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Net Income, Pretax	$ 84,482	$ 81,060	$ 162,260	$ 163,630
Net Income, Tax	26,173	24,476	49,815	49,907
Net income	58,309	56,584	112,445	113,723
Changes in unrealized securities' holding gains/(losses), before Tax	31,489	(28,642)	79,868	5,475
Changes in unrealized securities' holding gains/(losses), Tax	11,431	(10,024)	28,994	1,916
Changes in unrealized securities' holding gains/(losses), After-tax	20,058	(18,618)	50,874	3,559
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity, before Tax	(221)	(575)	(1,072)	(1,079)
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity, Tax	(79)	(203)	(14)	(378)
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity , Net of Tax	(142)	(372)	(1,058)	(701)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, before Tax	(2,164)	(567)	(2,459)	(921)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, Tax	(786)	(198)	(892)	(322)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, Net of Tax	1,378	369	1,567	599
Net change in unrealized gains/(losses) on securities available for sale, before Tax	29,104	(29,784)	76,337	3,475
Net change in unrealized gains/(losses) on securities available for sale, Tax	10,566	(10,425)	28,088	1,216
Net change in unrealized gains/(losses) on securities available for sale, Net of Tax	18,538	(19,359)	48,249	2,259
Amortization of actuarial losses/(gains), before Tax	1,076	1,138	3,244	2,276
Amortization of actuarial losses/(gains), Tax	390	399	1,163	797
Amortization of actuarial losses/(gains), Net of Tax	686	739	2,081	1,479
Amortization of prior service cost reclassified to other noninterest expense, before Tax	(560)	410	(820)	820
Amortization of prior service cost reclassified to other noninterest expense, Tax	(204)	144	(291)	287
Amortization of prior service cost reclassified to other noninterest expense, After-tax	(356)	266	(529)	533
Net change from defined benefit pension plans, before Tax	516	1,548	2,424	3,096
Net change from defined benefit pension plans, Tax	186	543	872	1,084
Net change from defined benefit pension plans, Net of Tax	330	1,005	1,552	2,012
Total other comprehensive gains/(losses), before Tax	29,620	(28,236)	78,761	6,571
Total other comprehensive gains/(losses), Tax	10,752	(9,882)	28,960	2,300
Total other comprehensive gains/(losses), Net of Tax	18,868	(18,354)	49,801	4,271
Comprehensive Income, before Tax, Portion Attributable to Parent	114,102	52,824	241,021	170,201
Comprehensive Income, Tax, Portion Attributable to Parent	36,925	14,594	78,775	52,207
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 77,177	$ 38,230	$ 162,246	$ 117,994