Accounts and Notes Receivable and Credit Quality of Notes Receivable - Allowance for Doubtful Accounts Receivable (Details) (Notes receivable, USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Notes receivable
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 5.6
Charge-offs	(0.1)
Recoveries	0
Provision	2.6
Ending balance	8.1
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment [Roll Forward]
Beginning balance	5.6
Charge-offs	(0.1)
Recoveries	0
Provision	2.6
Ending balance	8.1
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment [Roll Forward]
Beginning balance	0
Charge-offs	0
Recoveries	0
Provision	0
Ending balance	$ 0