Commitments and Letters of Credit (Detail 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Commitments to Extend Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Legally Binding Commitments	$ 398.1	$ 481.4
Commitments and Letters of Credit	37,247.0	35,127.6
Standby Letters of Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commitments and Letters of Credit	$ 4,305.4	$ 4,468.1
Weighted average maturity of standby letters of credit	24 months	27 months
Secured by Cash Deposits or Participated to Others | Standby Letters of Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commitments and Letters of Credit	$ 147.1	$ 221.4