Borrowings (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			0 Months Ended	12 Months Ended		12 Months Ended			0 Months Ended	12 Months Ended		12 Months Ended						12 Months Ended			1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Nov. 20, 2012 3.75% senior notes due 2022	Dec. 31, 2013 3.75% senior notes due 2022	Dec. 31, 2012 3.75% senior notes due 2022	Dec. 31, 2013 3.75% senior notes due 2022 Change-in-control	Dec. 31, 2013 3.75% senior notes due 2022 Subsidiaries	Dec. 31, 2013 3.75% senior notes due 2022 Significant Observable Inputs (Level 2)	Dec. 09, 2010 5.125% senior notes due 2020	Dec. 31, 2013 5.125% senior notes due 2020	Dec. 31, 2012 5.125% senior notes due 2020	Dec. 31, 2013 5.125% senior notes due 2020 Change-in-control	Dec. 31, 2013 5.125% senior notes due 2020 Subsidiaries	Dec. 31, 2013 5.125% senior notes due 2020 Significant Observable Inputs (Level 2)	Dec. 31, 2013 6.125% senior notes due 2016	Dec. 31, 2012 6.125% senior notes due 2016	Dec. 31, 2013 6.125% senior notes due 2016 Significant Observable Inputs (Level 2)	Dec. 31, 2013 Revolving credit facility	Dec. 31, 2012 Revolving credit facility	Oct. 20, 2011 Revolving credit facility	Dec. 31, 2013 Industrial development and revenue bonds through 2018	Dec. 31, 2012 Industrial development and revenue bonds through 2018	Dec. 31, 2013 Other, including capital lease obligations	Dec. 31, 2012 Other, including capital lease obligations	Dec. 31, 2013 Uncommitted line of credit	Dec. 31, 2012 Uncommitted line of credit
Borrowings
Total long-term debt	$ 751.0	$ 752.3			$ 349.0	$ 348.9					$ 249.2	$ 249.1				$ 149.7	$ 149.6					$ 3.0	$ 4.5	$ 0.1	$ 0.2
Total long-term debt, net of current portion	751.0	752.3
Interest rate (as a percent)				3.75%	3.75%					5.125%	5.125%					6.125%
Unamortized discount				(1.1)	(1.0)	(1.1)				(1.1)	(0.8)	(0.9)				(0.3)	(0.4)
Par value of senior notes				350.0	350.0					250.0	250.0					150.0
Proceeds from issuance of debt				348.9						248.9
Issuance costs including underwriter's, credit rating agencies' and attorneys' fees and other costs, which are included in other long-term assets	0.6	2.9	1.8	2.9						1.9
Long-term debt redemption price, description of variable discount rate					Treasury Rate						Treasury Rate
Long-term debt redemption price, basis spread on variable discount rate (as a percent)					0.35%						0.35%
Percentage of principal amount at which the entity may redeem some or all of the notes prior to specified date					100.00%						100.00%
Percentage of principal amount at which the entity may redeem some or all of the notes after specified date					100.00%						100.00%
Percentage of the principal amount at which the notes are redeemable							101.00%						101.00%
Subsidiaries indebtedness								3.1						3.1
Fair value of notes									326.3						259.8			163.8
Maximum borrowing capacity																					600.0					45.0	45.0
Remaining borrowing capacity																			600.0
Repayment of debt																						1.5
Average interest rate (as a percent)																				1.30%		1.09%	1.22%				1.58%
Interest on borrowings																			0
Amount outstanding																										0
Outstanding issued letters of credit	29.7
Interest income	0.5	0.5	0.5
Cash payments for interest	35.0	25.7	23.0
Long-term debt, by maturity
2016	150.0
2018	3.0
2020	250
2022	$ 350.0