Stock Incentive Plans - Performance Share Plans (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incremental modification expense				$ 5.5
Performance Share Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance share plan expense		$ 12.2	$ 11.4	$ 10.8
Performance share plan, shares issued in period	[1]			545,375

[1] Shares were issued in February of the following year.