Income Tax Expense - Unrecognized Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Unrecognized Tax Benefits
Unrecognized tax benefit, if recognized, would have an impact on effective tax rate	$ 1.9
Payment of interest and penalties accrued	0.4	0.4
Activity for unrecognized tax benefits
Balance at beginning of period	1.8	1.9	1.7
Tax positions related to current year additions	0	0	0.2
Additions for tax positions of prior years	7.2	0.1	0.2
Tax positions related to prior years reductions	(0.8)	0	0
Reductions due to lapse of statute of limitations on tax positions	(0.1)	0	0
Settlements	0	(0.2)	(0.2)
Balance at end of period	$ 8.1	$ 1.8	$ 1.9