Debt And Credit Facilities (Schedule Of Long-Term Debt) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Debt Instrument [Line Items]
Revolving loans drawn			$ 0
Term Loan, Amount Paid as of Reporting Date	278,000,000
Private Placement [Member]
Debt Instrument [Line Items]
Face Amount	325,000,000		325,000,000
Term Loan1.250 Million Member
Debt Instrument [Line Items]
Type	Variable
Average Annual Interest Rate	1.40%
Final Maturity	2016
Face Amount	972,000,000
Total Long-term Debt	897,200,000	[1]
Current Portion of term loan	74,800,000
Senior Notes 700 Million Due 2021 [Member]
Debt Instrument [Line Items]
Type	Fixed
Average Annual Interest Rate	4.88%
Final Maturity	2021
Face Amount	700,000,000
Total Long-term Debt	699,300,000	[2]
Unamortized discount	700,000
Imputed interest rate	4.89%
Senior Notes 500 Million Due 2020 Member
Debt Instrument [Line Items]
Type	Fixed		Fixed
Average Annual Interest Rate	4.80%		4.80%
Final Maturity	2020		2020
Face Amount	500,000,000		500,000,000
Total Long-term Debt	499,100,000	[3]	499,000,000	[3]
Unamortized discount	900,000		1,000,000
Imputed interest rate	4.83%
Senior Notes 500 Million Due 2040 Member
Debt Instrument [Line Items]
Type			Fixed
Average Annual Interest Rate			6.25%
Final Maturity			2040
Face Amount			500,000,000
Total Long-term Debt			491,300,000	[4]
Unamortized discount			8,700,000
Senior Notes 800 Million Due 2040 Member
Debt Instrument [Line Items]
Type	Fixed
Average Annual Interest Rate	6.25%
Final Maturity	2040
Face Amount	800,000,000
Total Long-term Debt	790,100,000	[4]
Unamortized discount	9,900,000
Imputed interest rate	6.38%
Senior Notes 400 Million [Member]
Debt Instrument [Line Items]
Type	Fixed		Fixed
Average Annual Interest Rate	5.90%		5.90%
Final Maturity	2020		2020
Face Amount	400,000,000		400,000,000
Total Long-term Debt	398,000,000	[5]	397,800,000	[5]
Unamortized discount	2,000,000		2,200,000
Imputed interest rate	5.98%
Series2008a Tranche [Member]
Debt Instrument [Line Items]
Type	Fixed		Fixed
Average Annual Interest Rate	6.31%		6.31%
Final Maturity	2013		2013
Face Amount	270,000,000		270,000,000
Total Long-term Debt	270,000,000		270,000,000
Series2008a Tranche B [Member]
Debt Instrument [Line Items]
Type	Fixed		Fixed
Average Annual Interest Rate	6.59%		6.59%
Final Maturity	2015		2015
Face Amount	55,000,000		55,000,000
Total Long-term Debt	55,000,000		55,000,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Type	Variable		Variable
Final Maturity	2016		2012
Face Amount	1,750,000,000		600,000,000
Total Long-term Debt		[6]		[6]
Principal amount of letter of credit obligations	23,500,000		64,700,000
Credit facility remaining capacity	1,726,500,000		535,300,000
Outstanding bank commitments on the multi-option facility	$ 23,500,000		$ 64,700,000

[1] As of December 31, 2011, $278.0 million had been paid down on the original $1.25 billion term loan and of the remaining term loan $74.8 million was classified as Current portion of term loan. The current classification is based upon the principal payment terms of the arrangement requiring principal payments on each three-month anniversary following the funding of the term loan.

[2] As of December 31, 2011, the $700 million 4.875 percent senior notes were recorded at a par value of $700 million less unamortized discounts of $0.7 million, based on an imputed interest rate of 4.89 percent.

[3] As of December 31, 2011 and December 31, 2010, the $500 million 4.80 percent senior notes were recorded at a par value of $500 million less unamortized discounts of $0.9 million and $1.0 million, respectively, based on an imputed interest rate of 4.83 percent.

[4] As of December 31, 2011 and December 31, 2010, the $800 million and $500 million 6.25 percent senior notes were recorded at par values of $800 million and $500 million, respectively, less unamortized discounts of $9.9 million and $8.7 million, respectively, based on an imputed interest rate of 6.38 percent.

[5] As of December 31, 2011 and December 31, 2010, the $400 million 5.90 percent senior notes were recorded at a par value of $400 million less unamortized discounts of $2.0 million and $2.2 million, respectively, based on an imputed interest rate of 5.98 percent.

[6] As of December 31, 2011 and December 31, 2010, no revolving loans were drawn under the credit facility and the principal amount of letter of credit obligations totaled $23.5 million and $64.7 million, respectively, thereby reducing available borrowing capacity to $1,726.5 million and $535.3 million, respectively.