Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Alternative minimum tax and other credit carryforwards	$ 341.6	$ 233.4
Accrued and unfunded compensation and employee benefits	197.0	166.9
Amortizable intangible assets	39.4	62.0
Compensation expense related to stock options	12.6	14.7
Accrued liabilities	34.3	31.0
Accrued pension liability	23.4	24.3
Investments	9.5	10.0
Net operating loss carryforwards	22.1	12.9
Deferred rent liability	8.7	8.5
Other	7.7	4.8
Total deferred tax assets	696.3	568.5
Valuation allowance for deferred tax assets	(52.8)	(73.7)
Deferred tax assets	643.5	494.8
Nondeductible amortizable intangible assets	307.1	338.7
Investment-related partnerships	28.7	26.6
Depreciable fixed assets	11.7	8.8
Other prepaid items	4.6	4.3
Total deferred tax liabilities	352.1	378.4
Net deferred tax assets	$ 291.4	$ 116.4