Borrowings (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Interest expense and interest income [Abstract]
Interest expense	$ 125,995,000	$ 124,783,000	$ 115,324,000
Interest income	(4,854,000)	(9,258,000)	(8,953,000)
Interest expense, net	121,141,000	115,525,000	106,371,000
Letters of Credit [Abstract]
Letters of Credit Outstanding, Amount	96,725,000
Letters of Credit Expiration Dates	2013 through 2017
Maturities of Long-term Debt [Abstract]
2013	3,266,000
2014	2,645,000
2015	299,441,000
2016	0
2017	0
2018 and thereafter	1,887,264,000
Short-term borrowings [Abstract]
Current installments	(3,266,000)	(1,022,000)
Commercial Paper	607,500,000	0
Total short-term debt	610,766,000	1,022,000
Long-term borrowings [Abstract]
Long-term Debt	2,192,616,000	2,187,252,000
Proceeds from long-term debt, net of discount and issuance costs	0	788,971,000	0
Long-term debt	2,189,350,000	2,186,230,000
Line of Credit Facility [Abstract]
Line of credit facility, interest rate description	At the Company's election, loans under the Credit Agreement will bear interest at a Eurodollar or Sterling rate based on LIBOR, plus an applicable margin ranging from 0.565% to 1.225% (subject to adjustment based on the credit rating accorded the Company's senior unsecured debt by S&P and Moody's), or at a base rate pursuant to a formula defined in the Credit Agreement.
Line of credit facility, covenant terms	the Credit Agreement requires the Company to pay a facility fee and imposes various restrictions on the Company such as, among other things, the requirement for the Company 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 December 31, 2012 and had a coverage ratio of 13.9 to 1
Oustanding balance on five-year non-interest bearing amortizing loan		51,214,000
Net loss on extinguishment of non-interest bearing amortizing loan			4,343,000
Note due 2011 [Member]
Long-term borrowings [Abstract]
Debt instrument, stated interest rate (in hundredths)	6.50%
Debt instruments, maturity date	Feb. 15, 2011
Face amount of notes		400,000,000
Note due 2015 [Member]
Long-term borrowings [Abstract]
Long-term Debt	299,441,000	299,244,000
Debt instrument, stated interest rate (in hundredths)	4.875%
Term of debt instrument (in years)	10 years
Debt instruments, maturity date	Oct. 15, 2015
Note due 2018 [Member]
Long-term borrowings [Abstract]
Long-term Debt	348,268,000	347,938,000
Debt instrument, stated interest rate (in hundredths)	5.45%
Term of debt instrument (in years)	10 years
Debt instruments, maturity date	Mar. 15, 2018
Note due 2021 [Member]
Long-term borrowings [Abstract]
Long-term Debt	449,787,000	449,761,000
Debt instrument, stated interest rate (in hundredths)	4.30%
Term of debt instrument (in years)	10 years
Debt instruments, maturity date	Mar. 01, 2021
Face amount of notes		450,000,000
Note due 2038 [Member]
Long-term borrowings [Abstract]
Long-term Debt	247,771,000	247,683,000
Debt instrument, stated interest rate (in hundredths)	6.60%
Term of debt instrument (in years)	30 years
Debt instruments, maturity date	Mar. 15, 2038
Note due 2041 [Member]
Long-term borrowings [Abstract]
Long-term Debt	345,511,000	345,352,000
Debt instrument, stated interest rate (in hundredths)	5.375%
Term of debt instrument (in years)	30 years
Debt instruments, maturity date	Mar. 01, 2041
Face amount of notes		350,000,000
Debentures due 2028 [Member]
Long-term borrowings [Abstract]
Long-term Debt	199,448,000	199,414,000
Debt instrument, stated interest rate (in hundredths)	6.65%
Term of debt instrument (in years)	30 years
Debt instruments, maturity date	Jun. 01, 2028
Debenture due 2035 [Member]
Long-term borrowings [Abstract]
Long-term Debt	296,367,000	296,208,000
Debt instrument, stated interest rate (in hundredths)	5.375%
Term of debt instrument (in years)	30 years
Debt instruments, maturity date	Oct. 15, 2035
Other long term debt instruments [Member]
Long-term borrowings [Abstract]
Long-term Debt	6,023,000	1,652,000
Commercial Paper [Member]
Short-term borrowings [Abstract]
Short-term Debt, Weighted Average Interest Rate	0.20%
Credit Agreement [Member]
Line of Credit Facility [Abstract]
Unsecured revolving credit facility, maximum borrowing capacity	1,000,000,000
Credit facility expiration date	Nov. 10, 2016
Debentures [Member]
Long-term borrowings [Abstract]
Unamortized discount	4,185,000	4,379,000
Long-term Notes [Member]
Long-term borrowings [Abstract]
Unamortized discount	$ 9,222,000	$ 10,023,000