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, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Goodwill [Line Items]
Beginning Balance	$ 540.7	$ 537.8
Foreign Exchange Rates	(7.5)	2.9
Ending Balance	533.2	540.7
Corporate and Institutional Services
Goodwill [Line Items]
Beginning Balance	469.2	466.3
Foreign Exchange Rates	(7.4)	2.9
Ending Balance	461.8	469.2
Wealth Management
Goodwill [Line Items]
Beginning Balance	71.5		71.5
Foreign Exchange Rates	(0.1)
Ending Balance	$ 71.4		$ 71.5