Changes by Reporting Segment in Carrying Amounts of Goodwill, including Effect of Foreign Exchange Rates on Non-U.S.-Dollar-Denominated Balances (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Beginning Balance	$ 526.4	$ 533.2
Goodwill Acquired	11.8
Foreign Exchange Rates	(18.8)	(6.8)
Ending Balance	519.4	526.4
Corporate and Institutional Services
Goodwill [Roll Forward]
Beginning Balance	455.1	461.8
Goodwill Acquired	11.8
Foreign Exchange Rates	(18.5)	(6.7)
Ending Balance	448.4	455.1
Wealth Management
Goodwill [Roll Forward]
Beginning Balance	71.3	71.4
Goodwill Acquired	0.0
Foreign Exchange Rates	(0.3)	(0.1)
Ending Balance	$ 71.0	$ 71.3