Debt, Credit Facility (Details) (USD $)	9 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 1,500,000,000
Line of Credit Facility, Maximum Borrowing Capacity	2,250,000,000
Line of Credit Facility, Covenant Compliance	Our actual leverage for the four consecutive quarters ended September 30, 2014, was 2.6 which is below the maximum leverage of 3.5. Our actual interest coverage for the four consecutive quarters ended September 30, 2014, was 14.3 which is above the minimum interest coverage of 3.5. We were in compliance with all covenants at September 30, 2014.
Long-term Debt	1,170,600,000		1,188,800,000
Credit Agreement, covenant compliance, actual leverage ratio	2.6
Credit Agreement, covenant terms, maximum leverage ratio	3.5
Credit Agreement, covenant compliance, actual interest coverage ratio	14.3
Credit Agreement, covenant terms, minimum interest coverage ratio	3.5
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit Agreement, available funds	867,100,000
Letters of credit outstanding amount	93,200,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Initial commitment fee	0.125%
Long-term Debt	$ 0	[1]	$ 0	[1]
Base rate funds effective rate low end	0.50%
Base rate funds effective rate high range	1.00%

[1] Letters of credit outstanding under our credit facility totaled $93.2 million and available funds under this facility were $867.1 million at September 30, 2014 (which reflects borrowings under our commercial paper program).