Borrowings and Lines of Credit (Details) (USD $)	12 Months Ended																					12 Months Ended	3 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Note due 2011 [Member]	Dec. 31, 2010 Note due 2011 [Member]	Dec. 31, 2011 Note due 2015 [Member]	Dec. 31, 2010 Note due 2015 [Member]	Dec. 31, 2011 Note due 2018 [Member]	Dec. 31, 2010 Note due 2018 [Member]	Dec. 31, 2011 Note due 2021 [Member]	Dec. 31, 2010 Note due 2021 [Member]	Dec. 31, 2011 Note due 2038 [Member]	Dec. 31, 2010 Note due 2038 [Member]	Dec. 31, 2011 Note due 2041 [Member]	Dec. 31, 2010 Note due 2041 [Member]	Dec. 31, 2011 Debentures due 2028 [Member]	Dec. 31, 2010 Debentures due 2028 [Member]	Dec. 31, 2011 Debentures due 2035 [Member]	Dec. 31, 2010 Debentures due 2035 [Member]	Dec. 31, 2011 Other long term debt instruments [Member]	Dec. 31, 2010 Other long term debt instruments [Member]	Dec. 31, 2011 Credit Agreement [Member]	Dec. 31, 2010 Non-interest bearing amortizing loan [Member]	Dec. 31, 2011 Non-interest bearing amortizing loan [Member]	Dec. 31, 2011 Commercial Paper [Member]	Dec. 31, 2010 Commercial Paper [Member]	Dec. 31, 2011 Long-term notes [Member]	Dec. 31, 2010 Long-term notes [Member]	Dec. 31, 2011 Debentures [Member]	Dec. 31, 2010 Debentures [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate (in hundredths)				6.50%	6.50%	4.875%	4.875%	5.45%	5.45%	4.30%	4.30%	6.60%	6.60%	5.375%	5.375%	6.65%	6.65%	5.375%	5.375%
Term of debt instrument (in years)				10	10	10	10	10	10	10	10	30	30	30	30	30	30	30	30			5
Line of credit, 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 rating according 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.
Face amount of notes				$ 400,000,000						$ 450,000,000				$ 350,000,000
Proceeds from issuance of debt	788,971,000
Outstanding balance of note paid																								51,214,000
Net loss on extinguishment of non-interest bearing amortizing loan																							4,343,000
Notes payable and current portion of long-term debt	1,022,000	16,590,000																								15,000,000
Weighted average interest rate (in hundredths)																									0.20%	0.20%
Unamortized discounts																											10,023,000	5,764,000	4,379,000	4,572,000
Debt instrument, maturity date				Feb. 15, 2011	Feb. 15, 2011	Oct. 15, 2015	Oct. 15, 2015	Mar. 15, 2018	Mar. 15, 2018	Mar. 01, 2021	Mar. 01, 2021	Mar. 15, 2038	Mar. 15, 2038	Mar. 01, 2041	Mar. 01, 2041	Jun. 01, 2028	Jun. 01, 2028	Oct. 15, 2035	Oct. 15, 2035
Carrying amount	2,187,252,000	1,807,476,000		0	399,986,000	299,244,000	299,047,000	347,938,000	347,608,000	449,761,000	0	247,683,000	247,595,000	345,352,000	0	199,414,000	199,379,000	296,208,000	296,048,000	1,652,000	17,813,000
Current installments	(1,022,000)	(16,590,000)
Total long-term debt	2,186,230,000	1,790,886,000
Unsecured revolving credit facility, maximum borrowing capacity																						1,000,000,000
Scheduled maturities [Abstract]
Principal payments required on long-term debt in 2012	1,022,000
Principal payments required on long-term debt in 2013	511,000
Principal payments required on long-term debt in 2014	12,000
Principal payments required on long-term debt in 2015	299,248,000
Principal payments required on long-term debt 2016 and thereafter	1,886,459,000
Interest expense and interest income [Abstract]
Interest expense	124,878,000	115,388,000	116,159,000
Interest income	(9,282,000)	(8,966,000)	(15,687,000)
Interest expense, net	(115,596,000)	(106,422,000)	(100,472,000)
Outstanding in letters of credit with financial institutions	$ 59,891,000