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Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
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Income Tax Disclosure [Abstract] |  |
Alternative minimum tax and other credit carryforwards | $ 856.9 | $ 683.3
Accrued and unfunded compensation and employee benefits | 158.8 | 141.2
Amortizable intangible assets | 48.8 | 45.8
Compensation expense related to stock options | 12.2 | 13.4
Accrued liabilities | 63.8 | 64.8
Accrued pension liability | 11.5 | 16.8
Investments | 1.5 | 1.1
Net operating loss carryforwards | 36.8 | 30.5
Capital loss carryforwards | 12.2 | 12.9
Deferred rent liability | 4.2 | 4.8
Hedging instruments | 1.9 |
Other | 3.4 | 5.4
Total deferred tax assets | 1,212.0 | 1,020.0
Valuation allowance for deferred tax assets | (67.4) | (79.1)
Deferred tax assets | 1,144.6 | 940.9
Nondeductible amortizable intangible assets | 297.6 | 273.8
Investment-related partnerships | 13.6 | 17.6
Depreciable fixed assets | 25.4 | 26.5
Revenue recognition | 98.1 | 80.6
Hedging instruments |  | 3.8
Other prepaid items | 10.6 | 10.3
Total deferred tax liabilities | 445.3 | 412.6
Net deferred tax assets | $ 699.3 | $ 528.3

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