Securities (Amortized Cost And Estimated Fair Value Of Securities, Excluding Trading Securities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Held to Maturity, Amortized Cost	$ 365,603	$ 365,996	$ 341,034
Held to Maturity, Gross Unrealized Gains	37,226	38,465
Held to Maturity, Estimated Fair Value	402,829	404,461
Available for Sale, Amortized Cost	8,216,531	7,440,389
Available for Sale, Gross Unrealized Gains	351,931	349,514
Available for Sale, Gross Unrealized Losses	247	203
Available for Sale, Estimated Fair Value	8,568,215	7,789,700	5,662,211
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Held to Maturity, Amortized Cost	247,893	247,797
Held to Maturity, Gross Unrealized Gains	29,275	31,715
Held to Maturity, Estimated Fair Value	277,168	279,512
Available for Sale, Amortized Cost	3,018,660	2,020,621
Available for Sale, Gross Unrealized Gains	29,607	36,111
Available for Sale, Gross Unrealized Losses	219
Available for Sale, Estimated Fair Value	3,048,048	2,056,732
U.S. Government Agencies/Corporations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for Sale, Amortized Cost	250,000	250,000
Available for Sale, Gross Unrealized Gains	782	884
Available for Sale, Estimated Fair Value	250,782	250,884
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Held to Maturity, Amortized Cost	11,547	11,874
Held to Maturity, Gross Unrealized Gains	178	153
Held to Maturity, Estimated Fair Value	11,725	12,027
Available for Sale, Amortized Cost	2,967,744	3,135,064
Available for Sale, Gross Unrealized Gains	156,222	154,386
Available for Sale, Gross Unrealized Losses	1	180
Available for Sale, Estimated Fair Value	3,123,965	3,289,270
States And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Held to Maturity, Amortized Cost	105,163	105,325
Held to Maturity, Gross Unrealized Gains	7,773	6,597
Held to Maturity, Gross Unrealized Losses
Held to Maturity, Estimated Fair Value	112,936	111,922
Available for Sale, Amortized Cost	1,942,118	1,996,703
Available for Sale, Gross Unrealized Gains	165,320	158,133
Available for Sale, Gross Unrealized Losses	27	23
Available for Sale, Estimated Fair Value	2,107,411	2,154,813
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Held to Maturity, Amortized Cost	1,000	1,000
Held to Maturity, Gross Unrealized Losses
Held to Maturity, Estimated Fair Value	1,000	1,000
Available for Sale, Amortized Cost	38,009	38,001
Available for Sale, Gross Unrealized Losses
Available for Sale, Estimated Fair Value	$ 38,009	$ 38,001

For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading.

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Reference 8: http://www.xbrl.org/2003/role/presentationRef

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

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-URI http://asc.fasb.org/extlink&oid=6379932&loc=d3e22054-111558

+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details

- Definition

For an unclassified balance sheet, this item represents investments in debt securities which are categorized as held-to-maturity. The held-to-maturity category is for those securities that the entity has the positive intent and ability to hold until maturity.

+ References

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

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-Subparagraph (SX 210.9-03.6)

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+ Details

- Definition

This item represents the aggregate fair value of investments in debt securities as of the balance sheet date and which are categorized as held-to-maturity.

+ References+ Details

- Definition

As of the balance sheet date, the excess of fair value over carrying value (amortized cost) of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding gain.

+ References+ Details

- Definition

As of the balance sheet date, the excess of carrying value (amortized cost) over fair value of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding loss.

+ References+ Details