Long-Term Debt And Notes Payable (Components Of Debt) (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	5.00%
Net decrease in short-term debt	$ 0.0	$ 28.5
Long-term debt	$ 745.5		$ 745.3
2.75% Notes Due 2018
Debt Instrument [Line Items]
Maturity Year Of Debt Instrument	2018
Debt Instrument, Interest Rate, Stated Percentage	2.75%		2.75%
Long-term debt	$ 249.3		$ 249.2
Debt Instrument, Face Amount	250.0		250.0
Amortization of Debt Issuance Costs	(0.7)		(0.8)
Six Point Five Five Percent Notes Due 2036 [Member]
Debt Instrument [Line Items]
Long-term debt	198.0		198.0
Debt Instrument, Face Amount	200.0		200.0
Amortization of Debt Issuance Costs	(1.3)		(1.3)
Debt Instrument, Unamortized Discount	(0.7)		(0.7)
Four Point Four Five Percent Notes Due 2023 [Member]
Debt Instrument [Line Items]
Long-term debt	298.2		298.1
Debt Instrument, Face Amount	300.0		300.0
Amortization of Debt Issuance Costs	$ (1.8)		$ (1.9)
4.45% Notes Due 2023
Debt Instrument [Line Items]
Maturity Year Of Debt Instrument	2023
Debt Instrument, Interest Rate, Stated Percentage	4.45%		4.45%
6.55% Notes Due 2036
Debt Instrument [Line Items]
Maturity Year Of Debt Instrument	2036
Debt Instrument, Interest Rate, Stated Percentage	6.55%		6.55%

Maturity Year of Debt Instrument

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Amount of amortization expense attributable to debt issuance costs.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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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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Amount, after accumulated amortization, of debt discount.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The net cash inflow or outflow for borrowing having initial term of repayment within one year or the normal operating cycle, if longer.

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