Securities (Year End Securities Held to Maturity and Available for Sale) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	$ 2,956,381	$ 365,996
Held to Maturity, Gross Unrealized Gains	45,556	38,465
Held to Maturity, Gross Unrealized Losses	4,993
Held to Maturity, Estimated Fair Value	2,996,944	404,461
Available for Sale, Amortized Cost	5,990,577	7,440,389
Available for Sale, Gross Unrealized Gains	212,747	349,514
Available for Sale, Gross Unrealized Losses	25	203
Available for Sale, Estimated Fair Value	6,203,299	7,789,700
US Treasury [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	248,188	247,797
Held to Maturity, Gross Unrealized Gains	29,859	31,715
Held to Maturity, Gross Unrealized Losses
Held to Maturity, Estimated Fair Value	278,047	279,512
Available for Sale, Amortized Cost	3,020,115	2,020,621
Available for Sale, Gross Unrealized Gains	37,806	36,111
Available for Sale, Estimated Fair Value	3,057,921	2,056,732
US Government Agencies/Corporations [Member]
Schedule of Available-for-Sale Securities [Line Items]
Available for Sale, Amortized Cost		250,000
Available for Sale, Gross Unrealized Gains		884
Available for Sale, Estimated Fair Value		250,884
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	10,725	11,874
Held to Maturity, Gross Unrealized Gains	300	153
Held to Maturity, Gross Unrealized Losses
Held to Maturity, Estimated Fair Value	11,025	12,027
Available for Sale, Amortized Cost	2,382,514	3,135,064
Available for Sale, Gross Unrealized Gains	135,514	154,386
Available for Sale, Gross Unrealized Losses	25	180
Available for Sale, Estimated Fair Value	2,518,003	3,289,270
States and Political Subdivisions [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	2,696,468	105,325
Held to Maturity, Gross Unrealized Gains	15,397	6,597
Held to Maturity, Gross Unrealized Losses	4,993
Held to Maturity, Estimated Fair Value	2,706,872	111,922
Available for Sale, Amortized Cost	552,056	1,996,703
Available for Sale, Gross Unrealized Gains	39,427	158,133
Available for Sale, Gross Unrealized Losses		23
Available for Sale, Estimated Fair Value	591,483	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	35,892	38,001
Available for Sale, Estimated Fair Value	$ 35,892	$ 38,001

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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

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Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

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-Paragraph 4

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-Publisher FASB

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-Paragraph 1

-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