Statement of Comprehensive Income Statement of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Net Income, Pretax	$ 81,060	$ 85,484	$ 163,630	$ 162,787
Net Income, Tax	24,476	25,965	49,907	49,813
Net Income, After Tax	56,584	59,519	113,723	112,974
Changes in unrealized securities' holding gains/(losses), before Tax	(28,642)	22,456	5,475	40,500
Changes in unrealized securities' holding gains/(losses), Tax	(10,024)	7,860	1,916	14,175
Changes in unrealized securities' holding gains/(losses), Net of Tax	(18,618)	14,596	3,559	26,325
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity, before Tax	(575)	(494)	(1,079)	(988)
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity, Tax	(203)	(173)	(378)	(346)
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity , Net of Tax	(372)	(321)	(701)	(642)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, before Tax	(567)	(80)	(921)	(136)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, Tax	(198)	(28)	(322)	(48)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, Net of Tax	(369)	(52)	(599)	(88)
Net change in unrealized gains/(losses) on securities available for sale, before Tax	(29,784)	21,882	3,475	39,376
Net change in unrealized gains/(losses) on securities available for sale, Tax	(10,425)	7,659	1,216	13,781
Net change in unrealized gains/(losses) on securities available for sale, Net of Tax	(19,359)	14,223	2,259	25,595
Amortization of actuarial losses/(gains), before Tax	1,138	1,631	2,276	1,631
Amortization of actuarial losses/(gains), Tax	399	571	797	571
Amortization of actuarial losses/(gains), Net of Tax	739	1,060	1,479	1,060
Amortization of prior service cost reclassified to other noninterest expense, before Tax	(410)	(1,097)	(820)	(1,097)
Amortization of prior service cost reclassified to other noninterest expense, Tax	(144)	(383)	(287)	(383)
Amortization of prior service cost reclassified to other noninterest expense, Net of Tax	(266)	(714)	(533)	(714)
Net change from defined benefit pension plans, before Tax	1,548	2,728	3,096	2,728
Net change from defined benefit pension plans, Tax	543	954	1,084	954
Net change from defined benefit pension plans, Net of Tax	1,005	1,774	2,012	1,774
Total other comprehensive gains/(losses), before Tax	(28,236)	24,610	6,571	42,104
Total other comprehensive gains/(losses), Tax	(9,882)	8,613	2,300	14,735
Total other comprehensive gains/(losses), Net of Tax	(18,354)	15,997	4,271	27,369
Comprehensive Income, before Tax, Portion Attributable to Parent	52,824	110,094	170,201	204,891
Comprehensive Income, Tax, Portion Attributable to Parent	14,594	34,578	52,207	64,548
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	38,230	75,516	117,994	140,343
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