Fair Value Measurements - Carrying Amounts and Estimated Fair Value for Financial Instrument Assets (Liabilities) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Financial assets:
Cash and cash equivalents	$ 1,763,118	$ 1,672,934	$ 1,826,067	$ 1,986,615
Interest-bearing deposits at banks	3,299,185	1,651,138
Trading account assets	314,807	376,131
Loans and leases:
Allowance for credit losses	(916,768)	(916,676)	(927,117)	(925,860)
Loans and leases, net	63,218,310	63,156,483
Financial liabilities:
Noninterest-bearing deposits	(25,244,200)	(24,661,007)
Time deposits	(3,402,515)	(3,523,838)
Deposits at Cayman Islands office	(247,880)	(322,746)
Long-term borrowings	(6,251,197)	(5,108,870)
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets:
Cash and cash equivalents	1,689,900	1,596,877
Interest-bearing deposits at banks
Trading account assets	49,473	51,386
Investment securities	80,580	82,450
Loans and leases:
Commercial loans and leases
Commercial real estate loans
Residential real estate loans
Consumer loans
Allowance for credit losses
Loans and leases, net
Accrued interest receivable
Financial liabilities:
Noninterest-bearing deposits
Savings deposits and NOW accounts
Time deposits
Deposits at Cayman Islands office
Short-term borrowings
Long-term borrowings
Accrued interest payable
Trading account liabilities
Other financial instruments:
Commitments to originate real estate loans for sale
Commitments to sell real estate loans
Other credit-related commitments
Interest rate swap agreements used for interest rate risk management
Significant Observable Inputs (Level 2) [Member]
Financial assets:
Cash and cash equivalents	73,218	76,057
Interest-bearing deposits at banks	3,299,185	1,651,138
Trading account assets	265,334	324,745
Investment securities	9,997,771	8,384,106
Loans and leases:
Commercial loans and leases
Commercial real estate loans	38,305	67,505
Residential real estate loans	5,285,649	5,432,207
Consumer loans
Allowance for credit losses
Loans and leases, net	5,323,954	5,499,712
Accrued interest receivable	242,009	222,558
Financial liabilities:
Noninterest-bearing deposits	(25,244,200)	(24,661,007)
Savings deposits and NOW accounts	(39,804,771)	(38,611,021)
Time deposits	(3,420,917)	(3,542,789)
Deposits at Cayman Islands office	(247,880)	(322,746)
Short-term borrowings	(230,209)	(260,455)
Long-term borrowings	(6,388,067)	(5,244,902)
Accrued interest payable	(59,685)	(43,419)
Trading account liabilities	(216,366)	(249,797)
Other financial instruments:
Commitments to originate real estate loans for sale
Commitments to sell real estate loans	1,055	12,360
Other credit-related commitments
Interest rate swap agreements used for interest rate risk management	94,716	102,875
Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Cash and cash equivalents
Interest-bearing deposits at banks
Trading account assets
Investment securities	226,679	223,938
Loans and leases:
Commercial loans and leases	18,584,218	18,457,288
Commercial real estate loans	25,931,696	25,950,690
Residential real estate loans	3,448,055	3,435,665
Consumer loans	10,271,804	10,201,087
Allowance for credit losses
Loans and leases, net	58,235,773	58,044,730
Accrued interest receivable
Financial liabilities:
Noninterest-bearing deposits
Savings deposits and NOW accounts
Time deposits
Deposits at Cayman Islands office
Short-term borrowings
Long-term borrowings
Accrued interest payable
Trading account liabilities
Other financial instruments:
Commitments to originate real estate loans for sale	12,589	3,941
Commitments to sell real estate loans
Other credit-related commitments	(114,641)	(118,886)
Interest rate swap agreements used for interest rate risk management
Carrying Amount [Member]
Financial assets:
Cash and cash equivalents	1,763,118	1,672,934
Interest-bearing deposits at banks	3,299,185	1,651,138
Trading account assets	314,807	376,131
Investment securities	10,364,249	8,796,497
Loans and leases:
Commercial loans and leases	18,896,070	18,705,216
Commercial real estate loans	26,104,086	26,148,208
Residential real estate loans	8,774,095	8,928,221
Consumer loans	10,360,827	10,291,514
Allowance for credit losses	(916,768)	(916,676)
Loans and leases, net	63,218,310	63,156,483
Accrued interest receivable	242,009	222,558
Financial liabilities:
Noninterest-bearing deposits	(25,244,200)	(24,661,007)
Savings deposits and NOW accounts	(39,804,771)	(38,611,021)
Time deposits	(3,402,515)	(3,523,838)
Deposits at Cayman Islands office	(247,880)	(322,746)
Short-term borrowings	(230,209)	(260,455)
Long-term borrowings	(6,251,197)	(5,108,870)
Accrued interest payable	(59,685)	(43,419)
Trading account liabilities	(216,366)	(249,797)
Other financial instruments:
Commitments to originate real estate loans for sale	12,589	3,941
Commitments to sell real estate loans	1,055	12,360
Other credit-related commitments	(114,641)	(118,886)
Interest rate swap agreements used for interest rate risk management	94,716	102,875
Estimate Fair Value [Member]
Financial assets:
Cash and cash equivalents	1,763,118	1,672,934
Interest-bearing deposits at banks	3,299,185	1,651,138
Trading account assets	314,807	376,131
Investment securities	10,305,030	8,690,494
Loans and leases:
Commercial loans and leases	18,584,218	18,457,288
Commercial real estate loans	25,970,001	26,018,195
Residential real estate loans	8,733,704	8,867,872
Consumer loans	10,271,804	10,201,087
Allowance for credit losses
Loans and leases, net	63,559,727	63,544,442
Accrued interest receivable	242,009	222,558
Financial liabilities:
Noninterest-bearing deposits	(25,244,200)	(24,661,007)
Savings deposits and NOW accounts	(39,804,771)	(38,611,021)
Time deposits	(3,420,917)	(3,542,789)
Deposits at Cayman Islands office	(247,880)	(322,746)
Short-term borrowings	(230,209)	(260,455)
Long-term borrowings	(6,388,067)	(5,244,902)
Accrued interest payable	(59,685)	(43,419)
Trading account liabilities	(216,366)	(249,797)
Other financial instruments:
Commitments to originate real estate loans for sale	12,589	3,941
Commitments to sell real estate loans	1,055	12,360
Other credit-related commitments	(114,641)	(118,886)
Interest rate swap agreements used for interest rate risk management	$ 94,716	$ 102,875