DEBT (Debt) (Details) - USD ($)		3 Months Ended
		Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Feb. 28, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total short-term debt		$ 178,500,000	$ 133,000,000	$ 200,000,000
Total long-term debt - face value		2,846,390,000	2,846,396,000	2,846,412,000
Unamortized discounts and debt issuance costs		(65,777,000)	(67,016,000)	(70,703,000)
Total long-term debt - book value		2,780,613,000	2,779,380,000	2,775,709,000
Less current maturities		24,000	23,000	22,000
Total long-term debt - reported value		2,780,589,000	2,779,357,000	2,775,687,000
Estimated fair value of long-term debt		2,775,511,000	2,695,802,000	2,843,943,000
Bank Line of Credit [Member]
Debt Instrument [Line Items]
Total short-term debt	[1],[2]	$ 178,500,000	133,000,000	200,000,000
Maturity date		Dec. 31, 2021
Effective interest rate	[1],[2]	1.25%
Notes [Member] | Floating-Rate Notes Due 2020 [Member]
Debt Instrument [Line Items]
Total long-term debt - face value		$ 250,000,000	250,000,000	250,000,000
Maturity year		2020
Effective interest rate		3.61%
Notes [Member] | Floating-Rate Notes Due 2021 [Member]
Debt Instrument [Line Items]
Total long-term debt - face value		$ 500,000,000	500,000,000	500,000,000
Maturity year		2021
Effective interest rate		3.59%
Notes [Member] | 8.85% notes due 2021 [Member]
Debt Instrument [Line Items]
Total long-term debt - face value		$ 6,000,000	6,000,000	6,000,000
Interest rate		8.85%
Maturity year		2021
Effective interest rate		8.88%
Notes [Member] | 4.50% notes due 2025 [Member]
Debt Instrument [Line Items]
Total long-term debt - face value		$ 400,000,000	400,000,000	400,000,000
Interest rate		4.50%
Maturity year		2025
Effective interest rate		4.65%
Notes [Member] | 3.90% notes due 2027 [Member]
Debt Instrument [Line Items]
Total long-term debt - face value		$ 400,000,000	400,000,000	400,000,000
Interest rate		3.90%
Maturity year		2027
Effective interest rate		4.00%
Notes [Member] | 7.15% notes due 2037 [Member]
Debt Instrument [Line Items]
Total long-term debt - face value		$ 129,239,000	129,239,000	$ 129,239,000		$ 240,188,000
Interest rate		7.15%		7.15%
Maturity year		2037
Effective interest rate		8.05%
Notes [Member] | 4.50% notes due 2047 [Member]
Debt Instrument [Line Items]
Total long-term debt - face value		$ 700,000,000	700,000,000	$ 700,000,000
Interest rate		4.50%
Maturity year		2047
Effective interest rate		4.59%
Notes [Member] | 4.70% notes due 2048 [Member]
Debt Instrument [Line Items]
Total long-term debt - face value		$ 460,949,000	$ 460,949,000	460,949,000
Interest rate		4.70%	4.70%		4.70%
Maturity year		2048
Effective interest rate		5.42%
Other Notes [Member]
Debt Instrument [Line Items]
Total long-term debt - face value		$ 202,000	$ 208,000	$ 224,000
Effective interest rate		6.46%

[1] Borrowings on the bank line of credit are classified as short-term debt if we intend to repay within twelve months and as long-term debt if we have the intent and ability to extend payment beyond twelve months.

[2] The effective interest rate reflects the margin above LIBOR for LIBOR-based borrowings. We also paid upfront fees that are amortized to interest expense and pay fees for unused borrowing capacity and standby letters of credit.