Comprehensive Income (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Comprehensive Income.
Net Income, Before Tax	$ 49,588	$ 70,945	$ 112,434	$ 147,963
Net Income, Tax Effect	14,440	24,381	34,926	48,663
Net Income, Net of Tax	35,148	46,564	77,508	99,300
Other Comprehensive Income, Before Tax:
Net Unrealized Gains on Investment Securities, Before Tax	33,440	85,443	7,819	125,426
Reclassification of Investment Securities Net Gains Realized in Net Income, Before Tax	(1,431)	(14,951)	(8,132)	(34,972)
Net Unrealized Gains on Investment Securities, Net of Reclassification Adjustment, Before Tax	32,009	70,492	(313)	90,454
Amortization of Net Losses Related to Defined Benefit Plans, Before Tax	777	595	1,554	1,189
Change in Accumulated Other Comprehensive Income, Before Tax	32,786	71,087	1,241	91,643
Total Comprehensive Income, Before Tax	82,374	142,032	113,675	239,606
Other Comprehensive Income, Tax Effect:
Net Unrealized Gains on Investment Securities, Tax Effect	13,289	33,596	3,107	51,199
Reclassification of Investment Securities Net Gains Realized in Net Income, Tax Effect	(545)	(5,881)	(3,185)	(14,279)
Net Unrealized Gains on Investment Securities, Net of Reclassification Adjustment, Tax Effect	12,744	27,715	(78)	36,920
Amortization of Net Losses Related to Defined Benefit Plans, Tax Effect	200	215	506	428
Change in Accumulated Other Comprehensive Income, Tax Effect	12,944	27,930	428	37,348
Total Comprehensive Income, Tax Effect	27,384	52,311	35,354	86,011
Other Comprehensive Income, Net of Tax:
Net Unrealized Gains on Investment Securities, Net of Tax	20,151	51,847	4,712	74,227
Reclassification of Investment Securities Net Gains Realized in Net Income, Net of Tax	(886)	(9,070)	(4,947)	(20,693)
Net Unrealized Gains on Investment Securities, Net of Reclassification Adjustment, Net of Tax	19,265	42,777	(235)	53,534
Amortization of Net Losses Related to Defined Benefit Plans, Net of Tax	577	380	1,048	761
Change in Accumulated Other Comprehensive Income, Net of Tax	19,842	43,157	813	54,295
Total Comprehensive Income	$ 54,990	$ 89,721	$ 78,321	$ 153,595