Long-Term Debt (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Debt Instrument [Line Items]
Total debt	$ 3,218,922	$ 3,027,203	$ 1,781,981
Less: Current maturities of long-term debt and short-term facilities	(320,046)	(299,909)	(140,037)
Long-term debt	2,898,876	2,727,294	1,641,944
Revolving Facility, Due 2022
Debt Instrument [Line Items]
Total debt	170,000
6.60% Senior Notes, Due 2018
Debt Instrument [Line Items]
Total debt		299,871	299,676
7% Debentures, Due 2025
Debt Instrument [Line Items]
Total debt	124,225	124,180	124,134
6.25% Senior Notes, Due 2037
Debt Instrument [Line Items]
Total debt	228,063	228,033	228,003
4.25% Senior Notes, Due 2024
Debt Instrument [Line Items]
Total debt	396,104	395,814	395,532
4.250% Senior Notes, Due 2047
Debt Instrument [Line Items]
Total debt	591,457	591,688
3.500% Senior Notes, Due 2027
Debt Instrument [Line Items]
Total debt	494,522	494,352
Floating Rate Notes, Due 2020
Debt Instrument [Line Items]
Total debt	298,590	298,227	297,847
3.450% Senior Notes, Due 2027
Debt Instrument [Line Items]
Total debt	296,783	296,628	296,456
Floating Rate Notes, Due 2019
Debt Instrument [Line Items]
Total debt	298,889	298,102
Trade Receivable Facility
Debt Instrument [Line Items]
Total debt	320,000		140,000
Other Notes
Debt Instrument [Line Items]
Total debt	$ 289	$ 308	$ 333