Incentive Stock Plans - Summary of Performance Shares (Details) (Performance Shares [Member], USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares of Company stock reserved for performance shares	130,164		276,240		337,360
Weighted average fair value of performance share units granted	$ 40.33		$ 59.16		$ 56.36
Intrinsic value of outstanding performance share units	$ 5.8	[1]	$ 22.1	[1]	$ 36.3	[1]
Fair value of performance shares vested	0		7.0		22.2
Cash used to pay the minimum withholding tax requirements in lieu of receiving common shares	$ 1.8		$ 11.0		$ 7.2

[1] Intrinsic value of outstanding performance share units is based on the market price of the Company's stock at December 31, 2014.