Fair Value Measurements, Fair Value of Non financial Assets and Liabilities (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Asset Retirement Obligation, Roll Forward
Beginning balance	$ 4.1		$ 4.0		$ 3.8
Liabilities settled during the period	(0.2)		(0.5)		(0.1)
Accretion expense	0.4		0.3		0.3
Adjustment to accretion expense due to revisions to estimated cash flow and timing of expenditure	0.1	[1]	0.3	[1]	0
Ending balance	$ 4.4		$ 4.1		$ 4.0
(Decrease)/increase in basic earnings per share resulting from adjustment			$ (0.02)
(Decrease)/increase in diluted earnings per share resulting from adjustment			$ (0.02)
Weighted-average credit-adjusted risk-free rate	8.60%		8.70%

[1] The adjustment in 2013 did not have a material impact on the basic and diluted earnings per share for 2013. The adjustment in 2012 decreased both basic and diluted earnings per share for 2012 by approximately $0.02 per share.