Retirement Benefits - Schedule of One Percentage Point Change in Assumptions Effects on Projected Benefit Obligations (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Compensation and Retirement Disclosure [Abstract]
Effect of 1% decrease on net periodic benefit expense components	$ 22.8
Effect of 1% increase on net periodic benefit expense components	(19.5)
Effect of 1% decrease on projected benefit obligation	158.3
Effect of 1% increase on projected benefit obligation	(133.0)
Effect of 1% decrease on net periodic pension benefit expense components	10.0
Effect of 1% increase on net periodic pension benefit expense components	(10.0)
Effect of 1% decrease on net periodic medical and life insurance benefit expense	(0.3)
Effect of 1% increase on net periodic medical and life insurance benefit expense	0.4
Effect of 1% decrease on accumulated benefit obligation	(1.0)
Effect of 1% increase on accumulated benefit obligation	$ 1.1