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Effect of New Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Corporate income tax rate	21.00%	21.00%	35.00%
Operating lease right of use assets	$ 368.8			$ 379.6
Operating lease liabilities	410.7			420.3
Net rent related asset and liabilities				38.3
Cumulative effect of adoption of new accounting standards				2.4
Reclassification from accumulated other comprehensive income, current period, before tax	0.2
Accumulated Other Comprehensive Earnings (Loss) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of new accounting standards	$ (0.2)			$ (0.2)
Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect on retained earnings		$ 6.6

X

- Definition

Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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Amount of the cumulative effect on retained earnings net of related income tax effect.

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For a classified balance sheet, the cumulative difference between the rental income or payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense, by the lessor or lessee, respectively, more than one year after the balance sheet date. Such receivable is reduced by allowances attributable to, for instance, credit risk associated with a lessee.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Present value of lessee's discounted obligation for lease payments from operating lease.

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Amount before tax of reclassification adjustments of other comprehensive income (loss).

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