Borrowings (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Interest expense and interest income [Abstract]
Interest expense	$ 31,004,000	$ 31,099,000	$ 92,917,000	$ 94,210,000
Interest income	(767,000)	(700,000)	(2,156,000)	(4,065,000)
Interest expense, net	30,237,000	30,399,000	90,761,000	90,145,000
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount	121,102,000		121,102,000
Short-term borrowings [Abstract]
Current installments	3,235,000		3,235,000		3,266,000
Commercial Paper	668,900,000		668,900,000		607,500,000
Debt, Current	672,135,000		672,135,000		610,766,000
Long-term borrowings [Abstract]
Carrying amount of long-term debt	2,193,391,000		2,193,391,000		2,192,616,000
Long-term debt (noncurrent)	2,190,156,000		2,190,156,000		2,189,350,000
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 September 30, 2013, and it expects to remain in compliance with all of its debt covenants.
Note due 2015 [Member]
Long-term borrowings [Abstract]
Long-term debt	299,589,000		299,589,000		299,441,000
Debt instruments, maturity date			Oct. 15, 2015
Debt instrument, stated interest rate (in hundredths)	4.875%		4.875%
Term of debt instrument (in years)			10 years
Note due 2018 [Member]
Long-term borrowings [Abstract]
Long-term debt	348,515,000		348,515,000		348,268,000
Debt instruments, maturity date			Mar. 15, 2018
Debt instrument, stated interest rate (in hundredths)	5.45%		5.45%
Term of debt instrument (in years)			10 years
Note due 2021 [Member]
Long-term borrowings [Abstract]
Long-term debt	449,806,000		449,806,000		449,787,000
Debt instruments, maturity date			Mar. 01, 2021
Debt instrument, stated interest rate (in hundredths)	4.30%		4.30%
Term of debt instrument (in years)			10 years
Note due 2038 [Member]
Long-term borrowings [Abstract]
Long-term debt	247,837,000		247,837,000		247,771,000
Debt instruments, maturity date			Mar. 15, 2038
Debt instrument, stated interest rate (in hundredths)	6.60%		6.60%
Term of debt instrument (in years)			30 years
Note due 2041 [Member]
Long-term borrowings [Abstract]
Long-term debt	345,631,000		345,631,000		345,511,000
Debt instruments, maturity date			Mar. 01, 2041
Debt instrument, stated interest rate (in hundredths)	5.375%		5.375%
Term of debt instrument (in years)			30 years
Debentures due 2028 [Member]
Long-term borrowings [Abstract]
Long-term debt	199,474,000		199,474,000		199,448,000
Debt instruments, maturity date			Jun. 01, 2028
Debt instrument, stated interest rate (in hundredths)	6.65%		6.65%
Term of debt instrument (in years)			30 years
Debenture due 2035 [Member]
Long-term borrowings [Abstract]
Long-term debt	296,486,000		296,486,000		296,367,000
Debt instruments, maturity date			Oct. 15, 2035
Debt instrument, stated interest rate (in hundredths)	5.375%		5.375%
Term of debt instrument (in years)			30 years
Other long term debt instruments [Member]
Long-term borrowings [Abstract]
Long-term debt	6,053,000		6,053,000		6,023,000
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		$ 1,000,000,000
Minimum [Member]
Line of Credit Facility [Abstract]
Line of Credit Facility, Expiration Date			Dec. 31, 2013
Maximum [Member]
Line of Credit Facility [Abstract]
Line of Credit Facility, Expiration Date			Dec. 31, 2018