Stock Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company recognized total stock compensation expense, net of forfeitures	$ 27.4	$ 22.1	$ 42.5
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested, beginning balance	1,500,000	1,600,000
Nonvested, ending balance	1,400,000	1,500,000	1,600,000
Director Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 1.3	$ 1.0	$ 1.2
Intrinsic value of the unvested				$ 1,200,000.0
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	5 months
Number of shares granted	17,000	24,000	26,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized				$ 0.6
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested, beginning balance	24,000	26,000	21,000
Vested during period	(19,000)	(26,000)	(21,000)
Forfeited during period	0	0	0
Nonvested, ending balance	22,000	24,000	26,000
Restricted Share Activity [Roll Forward]
Nonvested, beginning balance, value	$ 1.2	$ 1.2	$ 1.1
Granted during period, value	1.4	1.2	1.2
Vested during period, value	(1.0)	(1.2)	(1.1)
Forfeited during period, value	0.0	0.0	0.0
Nonvested, ending balance, value	$ 1.2	$ 1.2	$ 1.1	$ 1.6
Market Based LTIA [Member] \| Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted	156,279	292,160	206,132
Grant Date Of Fair Value Of Shares Granted	$ 14.1	$ 15.0	$ 10.9
Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of the unvested				$ 80,000,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	1 year 9 months
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized				$ 32.1
Long Term Incentive Plan [Member] \| Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 26.1	21.1	41.3
Grant Date Value Of Shares Vested		$ 14.9	$ 14.9
Shares Vested		422,422	503,543
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested, beginning balance	1,453,000	1,557,000	1,837,000
Granted during period	451,000	644,000	830,000
Vested during period	(465,000)	(655,000)	(830,000)
Forfeited during period	(48,000)	(93,000)	(280,000)
Nonvested, ending balance	1,391,000	1,453,000	1,557,000
Restricted Share Activity [Roll Forward]
Nonvested, beginning balance, value	$ 73.4	$ 67.3	$ 64.4
Granted during period, value	39.7	35.5	38.3
Vested during period, value	(24.1)	(25.0)	(24.5)
Forfeited during period, value	(3.0)	(4.4)	(10.9)
Nonvested, ending balance, value	$ 73.4	$ 67.3	$ 64.4	$ 86.0
Service Based LTIA [Member] \| Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted	295,482	352,043	623,620
Grant Date Of Fair Value Of Shares Granted	$ 25.6	$ 20.4	$ 27.4

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Restricted Share Activity [Roll Forward]

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total value of forfeitures related to restricted stock awards forfeited during the period.

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The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Per share weighted average intrinsic value of equity-based compensation awards not vested. Excludes stock and unit options.

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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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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Net number of share options (or share units) granted during the period.

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Value, before forfeitures, of stock or other type of equity granted of any equity-based compensation plan other than an employee stock ownership plan (ESOP).

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