Debt (Details) (USD $)																	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 2.35% senior notes due September 2016	Dec. 31, 2013 2.35% senior notes due September 2016	Jun. 30, 2014 6.15% senior notes due February 2018	Dec. 31, 2013 6.15% senior notes due February 2018	Jun. 30, 2014 9.25% senior notes due January 2019	Dec. 31, 2013 9.25% senior notes due January 2019	Jun. 30, 2014 5.00% senior notes due September 2020	Dec. 31, 2013 5.00% senior notes due September 2020	Jun. 30, 2014 4.625% senior notes due September 2021	Dec. 31, 2013 4.625% senior notes due September 2021	Jun. 30, 2014 5.10% senior notes due September 2023	Dec. 31, 2013 5.10% senior notes due September 2023	Jun. 30, 2014 Revolving Credit Facility	Dec. 31, 2013 Revolving Credit Facility	Jun. 30, 2014 Revolving Credit Facility Minimum	Jun. 30, 2014 Commercial paper	Dec. 31, 2013 Commercial paper
Long-term debt
Senior Notes			$ 349,853,000	$ 349,820,000	$ 970,541,000	$ 969,928,000	$ 339,607,000	$ 339,607,000	$ 698,100,000	$ 697,947,000	$ 698,268,000	$ 698,148,000	$ 348,829,000	$ 348,765,000
Revolving credit facility															110,000,000	170,000,000
Other	227,000	10,243,000
Long-term Debt	3,956,497,000	3,914,302,000
Less: Current portion	207,000	10,185,000
Long-term debt	3,956,290,000	3,904,117,000																441,072,000	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																		$ 441,100,000
Weighted average interest rate on revolving credit facilities (as a percent)															1.45%			0.33%
Remaining period to maturity																	1 year