Debt (Details) (USD $)	3 Months Ended		6 Months Ended			6 Months Ended			1 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 Revolving Credit Facility [Member]	Jun. 30, 2013 Private Placement [Member]	Nov. 23, 2010 Private Placement [Member]	Jul. 31, 2013 Term Loan [Member]	Jun. 30, 2013 Term Loan [Member]	Jun. 30, 2013 Term Loan [Member]	Jun. 30, 2013 Revolving credit facility and term loan agreement [Member]	Nov. 23, 2010 Two Point Six Percent Notes, Due November Two Thousand Fifteen [Member]	Nov. 23, 2010 Four Point Zero Three Percent Notes, Due November Two Thousand Twenty [Member]	Nov. 23, 2010 Four Point One Eight Percent Notes, Due November Two Thousand Twenty Two [Member]	Jun. 30, 2009 Five Point Six Two Five Percent Notes, Due March Two Thousand Fourteen [Member]	Jun. 30, 2009 Six Point Five Percent Notes Due March Two Thousand Nineteen [Member]	Mar. 31, 2008 Four Point Eight Percent Notes Due March Two Thousand Thirteen [Member]	Mar. 31, 2008 Five Point Seven Five Percent Notes, Due March Two Thousand Eighteen [Member]	Jun. 30, 2003 Four Point Two Percent Notes, Due July Two Thousand Eighteen [Member]	May 31, 2003 Four Point Six Two Five Percent Notes, Due May Two Thousand Thirteen [Member]	Jun. 30, 2013 Two Point Three Seven Five Percent Notes, Due March Two Thousand Sixteen [Member]	Jun. 30, 2013 Four Point Six Zero Percent Notes, Due March Two Thousand Twenty [Member]	Jun. 30, 2013 Five Point Zero Percent Notes, Due March Two Thousand Twenty-Three [Member]	Jun. 30, 2013 Six Point Nine Five Percent Notes, Due March Two Thousand Forty-Three [Member]
Debt Instrument [Line Items]
Revolving credit facility draw down amount without violating covenant	$ 1,000,000,000		$ 1,000,000,000
2014 Notes acceleration of interest-rate swap gain, expected	9,800,000
Line of Credit Facility, Maximum Borrowing Capacity	1,000,000,000		1,000,000,000							500,000,000	500,000,000
2010 Revolving Credit Facility					1,000,000,000
Term loan incremental draw down										50,000,000	50,000,000
Minimum Compliance Of Interest Coverage Ratio Numerator												4
Minimum Compliance Interest Coverage Ratio Denominator												1
Revolving credit facility draw down amount without violating covenant	1,000,000,000		1,000,000,000
Long-term Line of Credit, Noncurrent										170,000,000	170,000,000
Maximum leverage ratio numerator Dec 2013												4
Maximum leverage ratio denominator Dec 2013												1
Maximum leverage ratio numerator March 2014												3.75
Maximum leverage ratio denominator March 2014												1
Maximum leverage ratio numerator Dec 2014												3.5
Long-term Debt, Maturities, Repayment Terms										Pursuant to the term loan agreement, we are required to repay an amount equal to 25% of the aggregate remaining principal amount of the term loan on June 29, 2014, and the remaining outstanding principal amount of the term loan on June 29, 2015.
Term Loan prepayment percentage of proceeds received from incurrence of debt	50.00%		50.00%
Amount in excess requiring prepayment of Term Loan	0		0
Limits of subsidiary debt plus existing at February 28, 2013												500,000,000
Private Placement Notes								535,000,000
Debt Instrument, Face Amount													142,000,000	290,000,000	103,000,000	500,000,000	350,000,000	0	0	0	0	250,000,000	500,000,000	500,000,000	250,000,000
Debt Instrument, Interest Rate, Stated Percentage													2.60%	4.03%	4.18%	5.625%	6.50%	480.00%	575.00%	420.00%	462.50%	2.375%	4.60%	5.00%	6.95%
Private Notes prepayment percent	100.00%		100.00%
2014 Notes prepayment percent	100.00%		100.00%
2014 Notes accrued interest to be paid April 2013	3,400,000		3,400,000
2014 Notes Make Whole Premium	21,700,000		21,700,000
2014 Notes loss on debt extinguishment, expected	13,000,000
2014 Notes write-off debt issuance costs, expected	1,100,000
Commercial Paper Program	1,000,000,000		1,000,000,000
Commercial Paper	4,900,000		4,900,000
Debt Instrument, Credit Rating	Our long-term credit ratings are Baa2 (Stable Outlook) with Moody's and BBB- (Negative Outlook) with S&P, which are on the low end of investment grade, and BB+ (Stable Outlook) with Fitch, which is below investment grade. In February 2013, Fitch lowered their long-term credit rating from BBB- (Negative Outlook) to BB+ (Stable Outlook) and Moody's lowered their long-term credit rating from Baa1 (Negative Outlook) to Baa2 (Stable Outlook).
Line of Credit Facility, Amount Outstanding	0		0
Maximum leverage ratio denominator Dec 2014												1
Interest coverage ratio add back maximum of restructuring or legal or regulatory action												400,000,000
Private Notes accrued interest paid March 2013					6,900,000
Private Notes Make Whole Premium	68,000,000		68,000,000
Repayments of Long-term Debt									117,500,000		380,000,000
Loss on extinguishment of debt	13,000,000	0	86,000,000	0			71,400,000				1,600,000
Write off of Deferred Debt Issuance Cost						$ 1,200,000	$ 3,400,000