Commitments and Letters of Credit (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Commitments to Extend Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
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
Commercial Letters of Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commitments and Letters of Credit	$ 17.2	$ 20.8