Additional Details Related to Certain Balance Sheet Captions (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Other current assets
Prepaid taxes	$ 69.8	$ 65.4
Prepaid expenses	56.9	59.9
Other	37.0	47.2
Total other current assets	163.7	172.5
Other assets
Investments in joint ventures	25.8	21.6
Deposits for real-estate leases	12.5	11.3
Indemnification assets related to acquisitions	19.3	23.5
Fixed maturity and other open ended mutual funds	58.9	48.0
Other	56.7	41.5
Total other assets	173.2	145.9
Accounts payable and accrued liabilities
Salaries and benefits	69.3	86.5
Incentive compensation	$ 102.8	155.2
Profit sharing contribution		9.3
Customer credits, advanced payments and advanced billings	$ 19.0	17.0
Self-insurance reserves for wholly-owned insurance subsidiary	23.8	21.5	$ 27.6
Dividends	6.7	75.0
Professional service fees	53.7	47.0
Interest accrued on debt	20.7	45.0
Accounts payable	17.6	19.4
Income taxes	12.0	16.1
Pension and other post retirement employee benefits	5.1	5.1
Other	78.5	60.5
Total accounts payable and accrued liabilities	409.2	557.6
Other liabilities
Pension and other post retirement employee benefits	230.1	244.8
Deferred rent-non-current portion	99.5	104.2
Interest accrued on UTPs	29.0	20.8
Legacy and other tax matters	1.7	8.6
Other	57.0	52.5
Total other liabilities	$ 417.3	$ 430.9