Long-Term Debt And Notes Payable (Components Of Debt) (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 11, 2013
Debt Instrument [Line Items]
Facility fee	0.15%
Debt Instrument, Basis Spread on Variable Rate	5.00%
Long-term Commercial Paper	$ 500,000,000
number of days to maturity	397
Net decrease in short-term debt	$ 97,000,000	$ 0
Long-term debt	749,200,000		$ 749,200,000
Line of Credit Facility, Amended Maximum Borrowing Capacity	500,000,000
Short-term borrowings	$ 97,700,000		$ 100,800,000
Margin	0.10%
Rate for LIBOR loans	1.10%
2.75% Notes Due 2018
Debt Instrument [Line Items]
Maturity Year Of Debt Instrument	2018	2018
Debt Instrument, Interest Rate, Stated Percentage	2.75%		2.75%	2.75%
Long-term debt	$ 250,000,000		$ 250,000,000
Other Liabilities [Member]
Debt Instrument [Line Items]
Long-term debt	700,000		800,000
Commercial Paper [Member]
Debt Instrument [Line Items]
Long-term debt	97,000,000		0
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term debt	0		100,000,000
Six Point Five Five Percent Notes Due 2036 [Member]
Debt Instrument [Line Items]
Long-term debt	199,200,000		199,300,000
Four Point Four Five Percent Notes Due 2023 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				4.45%
Long-term debt	$ 300,000,000		$ 300,000,000
4.45% Notes Due 2023
Debt Instrument [Line Items]
Maturity Year Of Debt Instrument	2023	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	2036
Debt Instrument, Interest Rate, Stated Percentage	6.55%		6.55%