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Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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Income Tax Disclosure [Abstract] |  |
Alternative minimum tax and other credit carryforwards | $ 998.0 | $ 962.1
Accrued and unfunded compensation and employee benefits | 239.9 | 156.0
Amortizable intangible assets | 61.3 | 54.3
Compensation expense related to stock options | 14.4 | 11.3
Accrued liabilities | 65.7 | 63.9
Accrued pension liability | 9.3 | 9.9
Investments | 1.3 | 0.9
Net operating loss carryforwards | 36.1 | 37.2
Capital loss carryforwards | 9.0 | 12.6
Lease liabilities | 96.3 | 65.3
Hedging instruments | 34.6 | 11.7
Other | 2.8 | 4.3
Total deferred tax assets | 1,568.7 | 1,389.5
Valuation allowance for deferred tax assets | (94.9) | (80.5)
Deferred tax assets | 1,473.8 | 1,309.0
Nondeductible amortizable intangible assets | 316.9 | 322.4
Investment-related partnerships | 8.5 | 9.1
Depreciable fixed assets | 32.4 | 22.4
Right-of-use assets | 92.2 | 62.6
Revenue recognition | 33.1 | 63.7
Other prepaid items | 12.0 | 10.6
Total deferred tax liabilities | 495.1 | 490.8
Net deferred tax assets | $ 978.7 | $ 818.2

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