Borrowings (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Debt Disclosure [Abstract]
Interest expense	$ 33,005,000	$ 33,691,000
Interest income	(968,000)	(1,036,000)
Interest expense, net	32,037,000	32,655,000
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount	136,114,000
Short-term borrowings [Abstract]
Current installments	300,002,000		299,956,000
Commercial Paper	325,500,000		478,000,000
Debt, Current	625,502,000		777,956,000
Long-term borrowings [Abstract]
Carrying amount of long-term debt	2,517,876,000		2,552,997,000
Long-term debt (noncurrent)	2,217,874,000		2,253,041,000
Line of Credit Facility [Abstract]
Line of Credit Facility, Covenant Terms	Under the credit facility, the Company is required to maintain an interest coverage ratio of EBITDA to consolidated net interest expense of not less than 3.0 to 1.
Line of Credit Facility, Covenant Compliance	The Company was in compliance with this covenant and its other long-term debt covenants at March 31, 2015, and it expects to remain in compliance with all of its debt covenants.
Note due 2015 [Member]
Long-term borrowings [Abstract]
Long-term debt	299,885,000		299,836,000
Debt instruments, maturity date	Oct. 15, 2015
Debt instrument, stated interest rate (in hundredths)	4.875%
Term of debt instrument (in years)	10 years
Note due 2018 [Member]
Long-term borrowings [Abstract]
Long-term debt	349,010,000		348,928,000
Debt instruments, maturity date	Mar. 15, 2018
Debt instrument, stated interest rate (in hundredths)	5.45%
Term of debt instrument (in years)	10 years
Note due 2020 [Member]
Long-term borrowings [Abstract]
Long-term debt	328,632,000		363,970,000
Debt instruments, maturity date	Dec. 01, 2020
Debt instrument, stated interest rate (in hundredths)	2.125%
Term of debt instrument (in years)	7 years
Note due 2021 [Member]
Long-term borrowings [Abstract]
Long-term debt	449,846,000		449,839,000
Debt instruments, maturity date	Mar. 01, 2021
Debt instrument, stated interest rate (in hundredths)	4.30%
Term of debt instrument (in years)	10 years
Debentures due 2028 [Member]
Long-term borrowings [Abstract]
Long-term debt	199,526,000		199,517,000
Debt instruments, maturity date	Jun. 01, 2028
Debt instrument, stated interest rate (in hundredths)	6.65%
Term of debt instrument (in years)	30 years
Debenture due 2035 [Member]
Long-term borrowings [Abstract]
Long-term debt	296,725,000		296,685,000
Debt instruments, maturity date	Oct. 15, 2035
Debt instrument, stated interest rate (in hundredths)	5.375%
Term of debt instrument (in years)	30 years
Note due 2038 [Member]
Long-term borrowings [Abstract]
Long-term debt	247,970,000		247,948,000
Debt instruments, maturity date	Mar. 15, 2038
Debt instrument, stated interest rate (in hundredths)	6.60%
Term of debt instrument (in years)	30 years
Note due 2041 [Member]
Long-term borrowings [Abstract]
Long-term debt	345,870,000		345,830,000
Debt instruments, maturity date	Mar. 01, 2041
Debt instrument, stated interest rate (in hundredths)	5.375%
Term of debt instrument (in years)	30 years
Other long term debt instruments [Member]
Long-term borrowings [Abstract]
Long-term debt	412,000		444,000
Credit Agreement [Member]
Line of Credit Facility [Abstract]
Line of Credit Facility, Expiration Date	Nov. 10, 2016
Unsecured revolving credit facility, maximum borrowing capacity	$ 1,000,000,000
Minimum [Member]
Line of Credit Facility [Abstract]
Line of Credit Facility, Expiration Date	Dec. 31, 2015
Maximum [Member]
Line of Credit Facility [Abstract]
Line of Credit Facility, Expiration Date	Dec. 31, 2023