Commitments and Letters of Credit (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Commitments to Extend Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commitments and Letters of Credit	$ 32,768.1	$ 37,247.0
Standby Letters of Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commitments and Letters of Credit	3,846.1	4,305.4
Commercial Letters of Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commitments and Letters of Credit	$ 24.0	$ 17.2