Debt (Details) (USD $)	9 Months Ended				3 Months Ended					9 Months Ended	3 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Jul. 31, 2012	Dec. 31, 2011	Sep. 30, 2012 Credit Agreement [Member]	Sep. 30, 2012 Notes 2.70% due 2022 [Member]	Jul. 31, 2012 Notes 2.70% due 2022 [Member]	Sep. 30, 2012 Notes 5.75% due 2013 [Member]	Sep. 30, 2012 Notes 6.875% [Member]	Sep. 30, 2011 Unsecured Term Loan [Member]	Sep. 30, 2012 Credit Facility [Member] Credit Agreement [Member]	Sep. 30, 2012 Minimum [Member]	Sep. 30, 2012 Maximum [Member]	Sep. 30, 2012 Maximum [Member] Credit Facility [Member] Credit Agreement [Member]	Sep. 30, 2012 Dyrup [Member]
Schedule of Held-to-maturity Securities [Line Items]
Credit agreement term					5 years					3 years
Credit facility maximum borrowing capacity											$ 1,200,000,000
Line of Credit Facility, Terminated Amount											1,200,000,000
Amount of repaid debt										400,000,000
Credit facility additional borrowing capacity											300,000,000
Commitment fee percentage												0.08%	0.225%
Total indebtedness to total capitalization ratio requirement														60.00%
Principal amount							400,000,000
Stated interest rate							2.70%	5.75%	6.875%
Proceeds from issuance of debt						397,000,000
Short-term debt and current portion of long-term debt	636,000,000			108,000,000				600,000,000
Debt issuance cost						3,000,000
Settlement of forward starting swaps	(121,000,000)	0
Effective interest rate			5.80%
Business acquisition assumed debt	122,000,000														120,000,000
Repayment of acquired debt	119,000,000
Maturity of 6 7/8% notes	71,000,000	400,000,000
Payments of Debt Extinguishment Costs		$ 0