Contingencies, Commitments and Leases Leases (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2012	Dec. 31, 2013
Leases, Operating [Abstract]
Expiration date of lease on former headquarters building		Apr. 30, 2012
Rental expense		$ 1.5
Leases, Capital [Abstract]
New headquarters building lease term	17 years
Commencement date of capital lease on new headquarters building	May 01, 2012
Description of Lessee Leasing Arrangements, Capital Leases	Rental payments under the lease escalate at a rate of 3% per year during the lease term. The lease agreement does not include bargain renewal periods or material rent holidays and is not subject to contingent rent or other unusual provisions.
Assets under capital lease included in other property, plant and equipment	40.8		40.8
Assets under capital lease included in other accumulated depreciation, depletion and amortization	6.7		4.3
Current capital lease obligation	1.0		0.9
Noncurrent capital lease obligation	37.4		38.4
Future minimum payments and present value of net minimum payments under capital lease [Abstract]
2015	3.1
2016	3.5
2017	3.6
2018	3.7
2019	3.8
After 2019	41.0
Total minimum lease payments	58.7
Less: amount representing interest	(20.3)
Present value of minimum lease payments at year-end	$ 38.4