Securities (Detail 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Expected remaining maturities of debt securities available-for-sale, fair value
Fair Value	$ 5,210,388us-gaap_AvailableForSaleSecurities	$ 5,882,983us-gaap_AvailableForSaleSecurities
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Total of debt securities held-to-maturity, amortized cost	3,413,806us-gaap_HeldToMaturitySecurities	3,427,031us-gaap_HeldToMaturitySecurities
Total debt securities
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	1,083,708
Securities available-for-sale, Over 1 year through 5 years, fair value	4,104,631
Securities available-for-sale, Over 5 years through 10 years, fair value	17,544
Securities available-for-sale, Over 10 years, fair value	3,355
Fair Value	5,209,238	5,879,837
Expected remaining maturities of debt securities available-for-sale, amortized cost
Securities available-for-sale, One year or less, amortized cost	1,081,124
Securities available-for-sale, Over 1 year through 5 years, amortized cost	4,097,536
Securities available-for-sale, Over 5 years through 10 years, amortized cost	17,600
Securities available-for-sale, Over 10 years, amortized cost	3,400
Total of debt securities available-for-sale, amortized cost	5,199,660
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	1,180,154
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	1,989,301
Securities held-to-maturity, Over 10 years, amortized cost	244,351
Total of debt securities held-to-maturity, amortized cost	3,413,806
U.S. Treasury
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	98,400
Securities available-for-sale, Over 1 year through 5 years, fair value	17,507
Fair Value	115,907	116,926
Federal agency - Debt
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	597,445
Securities available-for-sale, Over 1 year through 5 years, fair value	622,775
Fair Value	1,220,220	1,398,581
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	132,829
Securities held-to-maturity, Over 10 years, amortized cost	153,752
Total of debt securities held-to-maturity, amortized cost	286,581	292,932
Federal agency - MBS
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, Over 1 year through 5 years, fair value	83,971
Securities available-for-sale, Over 5 years through 10 years, fair value	17,544
Fair Value	101,515	104,526
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	49,153
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	503,264
Securities held-to-maturity, Over 10 years, amortized cost	4,514
Total of debt securities held-to-maturity, amortized cost	556,931	553,589
CMOs - Federal agency
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	157,341
Securities available-for-sale, Over 1 year through 5 years, fair value	3,047,545
Fair Value	3,204,886	3,580,590
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	867,361
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	898,964
Total of debt securities held-to-maturity, amortized cost	1,766,325	1,811,574
CMOs - Non-agency
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	1,381
Securities available-for-sale, Over 1 year through 5 years, fair value	21,430
Fair Value	22,811	24,014
State and municipal
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	171,999
Securities available-for-sale, Over 1 year through 5 years, fair value	252,104
Securities available-for-sale, Over 10 years, fair value	3,355
Fair Value	427,458	479,031
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	177,608
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	454,244
Securities held-to-maturity, Over 10 years, amortized cost	86,085
Total of debt securities held-to-maturity, amortized cost	717,937	682,705
Other debt securities
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	57,142
Securities available-for-sale, Over 1 year through 5 years, fair value	59,299
Fair Value	116,441	176,169
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	86,032
Total of debt securities held-to-maturity, amortized cost	$ 86,032	$ 86,231

This item represents the cost of debt 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.

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

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Amount after adjustments of available-for-sale debt securities at cost, maturing after the tenth rolling twelve months following the latest balance sheet. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the sixth through tenth rolling twelve months following the latest balance sheet. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the second through fifth rolling twelve months following the latest balance sheet. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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