Post Retirement Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components of net periodic benefit costs:
Service cost	$ 6.8	$ 7.2	$ 4.8
Interest cost	2.2	2.5	4.6
Expected return on plan assets	(1.8)	(2.3)	(4.1)
Settlement loss recognized		10.2
Amortization of net loss	4.1	4.1	0.1
Net periodic benefit costs	$ 11.3	$ 21.7	$ 5.4