Debt (Details) (USD $)					3 Months Ended														9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 2.35% senior notes due September 2016	Dec. 31, 2013 2.35% senior notes due September 2016	Sep. 30, 2014 6.15% senior notes due February 2018	Dec. 31, 2013 6.15% senior notes due February 2018	Sep. 30, 2014 9.25% senior notes due January 2019	Dec. 31, 2013 9.25% senior notes due January 2019	Sep. 30, 2014 5.00% senior notes due September 2020	Dec. 31, 2013 5.00% senior notes due September 2020	Sep. 30, 2014 4.625% senior notes due September 2021	Dec. 31, 2013 4.625% senior notes due September 2021	Sep. 30, 2014 5.10% senior notes due September 2023	Dec. 31, 2013 5.10% senior notes due September 2023	Sep. 30, 2014 Revolving Credit Facility	Dec. 31, 2013 Revolving Credit Facility	Sep. 30, 2014 Commercial paper	Dec. 31, 2013 Commercial paper	Sep. 30, 2014 Commercial paper Minimum
Long-term debt
Senior Notes			$ 349,870,000	$ 349,820,000	$ 948,900,000	$ 969,928,000	$ 339,607,000	$ 339,607,000	$ 698,177,000	$ 697,947,000	$ 698,328,000	$ 698,148,000	$ 348,861,000	$ 348,765,000
Revolving credit facility															100,000,000	170,000,000
Other	215,000	10,243,000
Long-term Debt	4,255,332,000	3,914,302,000
Less: Current portion	196,000	10,185,000
Long-term debt	4,255,136,000	3,904,117,000															771,374,000	329,844,000
Interest rate on senior notes due (as a percent)			2.35%		6.15%		9.25%		5.00%		4.625%		5.10%
Aggregate amount of senior notes																	771,400,000
Weighted average interest rate on revolving credit facilities (as a percent)															1.46%		0.35%
Remaining period to maturity																			1 year
Principal amount redeemed					22,000,000
Payment of debt principal					25,700,000
Payment of debt accrued interest					600,000
Premium paid in the redemption					$ 3,100,000