Long-Term Debt (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Debt Instrument [Line Items]
Total debt	$ 3,028,108	$ 3,027,203	$ 1,846,294
Less: Current maturities of long-term debt and short-term facilities	(300,006)	(299,909)	(290,048)
Long-term debt	2,728,102	2,727,294	1,556,246
Revolving Facility, Due 2022
Debt Instrument [Line Items]
Total debt			210,000
6.60% Senior Notes, Due 2018
Debt Instrument [Line Items]
Total debt	299,967	299,871	299,579
7% Debentures, Due 2025
Debt Instrument [Line Items]
Total debt	124,203	124,180	124,112
6.25% Senior Notes, Due 2037
Debt Instrument [Line Items]
Total debt	228,048	228,033	227,989
4.25% Senior Notes, Due 2024
Debt Instrument [Line Items]
Total debt	395,959	395,814	395,392
4.250% Senior Notes, Due 2047
Debt Instrument [Line Items]
Total debt	591,416	591,688
Floating Rate Notes, Due 2017
Debt Instrument [Line Items]
Total debt			298,878
3.500% Senior Notes, Due 2027
Debt Instrument [Line Items]
Total debt	494,402	494,352
Floating Rate Notes, Due 2020
Debt Instrument [Line Items]
Total debt	298,408	298,227
3.450% Senior Notes, Due 2027
Debt Instrument [Line Items]
Total debt	296,705	296,628
Floating Rate Notes, Due 2019
Debt Instrument [Line Items]
Total debt	298,704	298,102
Trade Receivable Facility
Debt Instrument [Line Items]
Total debt			290,000
Other Notes
Debt Instrument [Line Items]
Total debt	$ 296	$ 308	$ 344