Supplementary Financial Statement Information - Allowance for Doubtful Accounts (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowance For Doubtful Accounts
Balance at beginning of year	$ 8.1	$ 9.1	$ 11.9
Increase (decrease) in allowance	0.9	(0.4)	(2.7)
Receivables written off	0	(0.6)	(0.1)
Balance at end of year	$ 9.0	$ 8.1	$ 9.1