Investment Securities (Securities with Unrealized Losses and Length of Impairment Period) (Details) (USD $) In Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2011	Dec. 31, 2010
Fair Value	$ 7,717,634	$ 7,294,303
Unrealized Losses	23,964	36,177
U.S. Government and Federal Agency Obligations [Member]
Fair Value	356,246	455,537
Unrealized Losses
Government-Sponsored Enterprise Obligations [Member]
Fair Value	264,553	201,895
Unrealized Losses	331	530
Government-Sponsored Enterprise Obligations [Member] \| Less Than 12 Months [Member]
Fair Value	42,078	10,850
Unrealized Losses	331	530
Government-Sponsored Enterprise Obligations [Member] \| 12 Months or Longer [Member]
Fair Value
Unrealized Losses
Government-Sponsored Enterprise Obligations [Member] \| Total [Member]
Fair Value	42,078	10,850
Unrealized Losses	331	530
State and Municipal Obligations [Member]
Fair Value	1,193,561	1,119,485
Unrealized Losses	13,599	16,643
State and Municipal Obligations [Member] \| Less Than 12 Months [Member]
Fair Value	177,677	345,775
Unrealized Losses	2,453	7,470
State and Municipal Obligations [Member] \| 12 Months or Longer [Member]
Fair Value	96,602	82,269
Unrealized Losses	11,146	9,173
State and Municipal Obligations [Member] \| Total [Member]
Fair Value	274,279	428,044
Unrealized Losses	13,599	16,643
Agency Mortgage-Backed Securities [Member]
Fair Value	2,913,805	2,491,199
Unrealized Losses	1,669	3,440
Agency Mortgage-Backed Securities [Member] \| Less Than 12 Months [Member]
Fair Value	238,483	660,326
Unrealized Losses	1,669	3,440
Agency Mortgage-Backed Securities [Member] \| 12 Months or Longer [Member]
Fair Value
Unrealized Losses
Agency Mortgage-Backed Securities [Member] \| Total [Member]
Fair Value	238,483	660,326
Unrealized Losses	1,669	3,440
Non-Agency Mortgage-Backed Securities [Member]
Fair Value	385,937	455,790
Unrealized Losses	7,987	14,513
Non-Agency Mortgage-Backed Securities [Member] \| Less Than 12 Months [Member]
Fair Value	38,749	15,893
Unrealized Losses	250	36
Non-Agency Mortgage-Backed Securities [Member] \| 12 Months or Longer [Member]
Fair Value	139,127	170,545
Unrealized Losses	7,737	14,477
Non-Agency Mortgage-Backed Securities [Member] \| Total [Member]
Fair Value	177,876	186,438
Unrealized Losses	7,987	14,513
Other Asset-Backed Securities [Member]
Fair Value	2,394,627	2,354,260
Unrealized Losses	378	1,051
Other Asset-Backed Securities [Member] \| Less Than 12 Months [Member]
Fair Value	299,909	487,822
Unrealized Losses	378	1,029
Other Asset-Backed Securities [Member] \| 12 Months or Longer [Member]
Fair Value		24,928
Unrealized Losses		22
Other Asset-Backed Securities [Member] \| Total [Member]
Fair Value	299,909	512,750
Unrealized Losses	378	1,051
Other Debt Securities [Member]
Fair Value	168,859	176,964
Unrealized Losses
Equity Securities [Member]
Fair Value	40,046	39,173
Unrealized Losses
Total Mortgage and Asset-Backed Securities [Member]
Fair Value	5,694,369	5,301,249
Unrealized Losses	10,034	19,004
Total Mortgage and Asset-Backed Securities [Member] \| Less Than 12 Months [Member]
Fair Value	577,141	1,164,041
Unrealized Losses	2,297	4,505
Total Mortgage and Asset-Backed Securities [Member] \| 12 Months or Longer [Member]
Fair Value	139,127	195,473
Unrealized Losses	7,737	14,499
Total Mortgage and Asset-Backed Securities [Member] \| Total [Member]
Fair Value	716,268	1,359,514
Unrealized Losses	10,034	19,004
Total Temporarily Impaired Securities [Member] \| Less Than 12 Months [Member]
Fair Value	796,896	1,520,666
Unrealized Losses	5,081	12,505
Total Temporarily Impaired Securities [Member] \| 12 Months or Longer [Member]
Fair Value	235,729	277,742
Unrealized Losses	18,883	23,672
Total Temporarily Impaired Securities [Member] \| Total [Member]
Fair Value	1,032,625	1,798,408
Unrealized Losses	$ 23,964	$ 36,177

For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading. Such securities are reported at fair value, with unrealized gains and losses excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain or loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.

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- Definition

This item represents the gross unrealized losses for securities which are categorized neither as held-to-maturity nor trading securities. Such gross unrealized losses are the excess of the carrying value of the Available-for-sale Securities over their fair value as of the reporting date. Such gross unrealized losses are included in other comprehensive income in the statement of shareholders' equity, unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.

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