Borrowings by contractual maturities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014
Debt Disclosure [Line Items]
Debt Maturities Repayments Of Principal Within Remainder Of Year	$ 1,380,584
Debt Maturities Repayments Of Principal In Year Two	203,175
Debt Maturities Repayments Of Principal In Year Three	700,167
Debt Maturities Repayments Of Principal In Year Four	194,033
Debt Maturities Repayments Of Principal In Year Five	107,296
Later years	944,710
Debt With No Stated Maturity	936,000
Borrowed Funds	4,465,965
Short-term Debt [Member]
Debt Disclosure [Line Items]
Debt Maturities Repayments Of Principal Within Remainder Of Year	31,200
Debt Maturities Repayments Of Principal In Year Two	0
Debt Maturities Repayments Of Principal In Year Three	0
Debt Maturities Repayments Of Principal In Year Four	0
Debt Maturities Repayments Of Principal In Year Five	0
Later years	0
Debt With No Stated Maturity	0
Borrowed Funds	31,200
Long-term Debt [Member]
Debt Disclosure [Line Items]
Debt Maturities Repayments Of Principal Within Remainder Of Year	16,905
Debt Maturities Repayments Of Principal In Year Two	29,040
Debt Maturities Repayments Of Principal In Year Three	247,105
Debt Maturities Repayments Of Principal In Year Four	79,033
Debt Maturities Repayments Of Principal In Year Five	107,296
Later years	944,710
Debt With No Stated Maturity	936,000
Borrowed Funds	2,360,089
Federal Funds Purchased And Securities Sold Under Agreements To Repurchase [Member]
Debt Disclosure [Line Items]
Debt Maturities Repayments Of Principal Within Remainder Of Year	1,332,479
Debt Maturities Repayments Of Principal In Year Two	174,135
Debt Maturities Repayments Of Principal In Year Three	453,062
Debt Maturities Repayments Of Principal In Year Four	115,000
Debt Maturities Repayments Of Principal In Year Five	0
Later years	0
Debt With No Stated Maturity	0
Borrowed Funds	$ 2,074,676