Components of Other Operating Expense (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components Of Other Operating Expense [Line Items]
Business Promotion			$ 83.6	$ 85.1	$ 79.7
FDIC Insurance Premiums			31.7	25.2	22.0
Staff Related			43.0	40.5	39.1
Other Intangibles Amortization			8.8	10.9	19.5
Other Expenses			197.3	166.3	111.8
Total Other Operating Expense			$ 364.4	328.0	$ 272.1
Total NAV funds				$ (45.8)
Net Asset Value (in dollars per share)				$ 1.00
Agreement To Settle Securities
Components Of Other Operating Expense [Line Items]
Litigation expense	$ 3.5	$ 46.5
Contractual Modifications
Components Of Other Operating Expense [Line Items]
Litigation expense		$ 18.6