Consolidated Statements of Comprehensive Income Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Net Income, Pretax	$ 77,778	$ 82,570
Net Income, Tax	23,642	25,431
Net income	54,136	57,139
Changes in unrealized securities' holding gains/(losses), before Tax	48,379	34,117
Changes in unrealized securities' holding gains/(losses), Tax	17,562	11,941
Changes in unrealized securities' holding gains/(losses), After-tax	30,817	22,176
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity, before Tax	(1,441)	(504)
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity, Tax	(147)	(176)
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity , Net of Tax	(1,294)	(328)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, before Tax	295	(354)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, Tax	107	(124)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, Net of Tax	(188)	230
Net change in unrealized gains/(losses) on securities available for sale, before Tax	47,233	33,259
Net change in unrealized gains/(losses) on securities available for sale, Tax	17,522	11,641
Net change in unrealized gains/(losses) on securities available for sale, Net of Tax	29,711	21,618
Amortization of actuarial losses/(gains), before Tax	2,168	1,138
Amortization of actuarial losses/(gains), Tax	773	398
Amortization of actuarial losses/(gains), Net of Tax	1,395	740
Amortization of prior service cost reclassified to other noninterest expense, before Tax	(260)	410
Amortization of prior service cost reclassified to other noninterest expense, Tax	(87)	143
Amortization of prior service cost reclassified to other noninterest expense, After-tax	(173)	267
Net change from defined benefit pension plans, before Tax	1,908	1,548
Net change from defined benefit pension plans, Tax	686	541
Net change from defined benefit pension plans, Net of Tax	1,222	1,007
Total other comprehensive gains/(losses), before Tax	49,141	34,807
Total other comprehensive gains/(losses), Tax	18,208	12,182
Total other comprehensive gains/(losses), Net of Tax	30,933	22,625
Comprehensive Income, before Tax, Portion Attributable to Parent	126,919	117,377
Comprehensive Income, Tax, Portion Attributable to Parent	41,850	37,613
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 85,069	$ 79,764