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	Mar. 31, 2015	Dec. 31, 2014
Goodwill [Line Items]
Total Goodwill	$ 527.3	$ 533.2
Corporate & Institutional Services
Goodwill [Line Items]
Total Goodwill	456.0	461.8
Wealth Management
Goodwill [Line Items]
Total Goodwill	$ 71.3	$ 71.4