Debt, Long-term (Details) (USD $)	9 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Debt Instrument [Line Items]
Total long-term debt	$ 1,170,600,000		$ 1,188,800,000
Less: debt maturing within one year	18,700,000		34,700,000
Total long-term debt, less current portion	1,151,900,000		1,154,100,000
Medium-term Notes	2,000,000,000
Line of Credit Facility, Current Borrowing Capacity	1,500,000,000
Line of Credit Facility, Maximum Borrowing Capacity	2,250,000,000
Medium-term Notes [Member]
Debt Instrument [Line Items]
Base rate funds effective rate low end	0.50%
Base rate funds effective rate high range	1.00%
Initial commitment fee	0.125%
Pollution Control and Industrial Revenue Bonds [Member]
Debt Instrument [Line Items]
Interest rate percentage, minimum	0.20%
Interest rate percentage, maximum	6.50%
Maturity date, minimum	2014
Maturity date, maximum	2035
Total long-term debt	158,000,000		174,000,000
Unamortized discount	200,000		200,000
Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate percentage, minimum	3.95%
Interest rate percentage, maximum	5.20%
Maturity date, minimum	2019
Maturity date, maximum	2024
Total long-term debt	998,000,000		997,800,000
Unamortized discount	2,000,000		2,200,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Interest rate percentage	2.50%
Debt Instrument, Maturity Year	2017
Total 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%
Initial commitment fee	0.125%
Foreign Debt [Member]
Debt Instrument [Line Items]
Interest rate percentage, minimum	0.00%
Interest rate percentage, maximum	9.30%
Maturity date, minimum	2014
Maturity date, maximum	2024
Total long-term debt	$ 14,600,000		$ 17,000,000

[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).