Commitments, Contingencies and Off-Balance Sheet Arrangements - Outstanding Letters of Credit, Financial Guarantees and Funding Commitments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Maximum Exposure	$ 46.1
Liability Recorded	9.7
Funding Commitment To Two Funds Expire In 2019 And 2023 Trigger [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Collateral	None
Compensation to Us	None
Maximum Exposure	2.9
Credit Support Under Letters Of Credit For Deductibles Due By Us On Our Own Insurance Coverage's Expires After 2019 Trigger [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Collateral	None
Compensation to Us	None
Maximum Exposure	11.3
Liability Recorded	9.7
Credit Enhancement Under Letters Of Credit For Our Captive Insurance Operations To Meet Minimum Statutory Capital Requirements Expires After 2019 [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Collateral	None
Compensation to Us	Reimbursement of LOC fees
Maximum Exposure	6.3
Credit Support Under Letters Of Credit For Clients Claim Funds Held By Our Bermuda Captive Insurance Operation In Fiduciary Capacity Expires After 2019 [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Collateral	None
Compensation to Us	Reimbursement of LOC fees
Maximum Exposure	5.0
Financial Guarantee Of Mortgage Loan To UK Based Employee Expires When Mortgage Balance Reduced Trigger [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Compensation to Us	None
Maximum Exposure	9.1
Financial Guarantees Of Loans To Thirty Seven Canadian Based Employees Expires When Loan Balances Reduced Trigger [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Compensation to Us	None
Maximum Exposure	$ 11.5