Retirement Benefit Plans (Components of net periodic benefit cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Retirement Plans [Member]
Service cost	$ 4.6	$ 5.4	$ 4.9
Interest cost	16.5	17.7	21.0
Expected return on plan assets	(21.7)	(22.9)	(24.6)
Amortization of prior service cost/(credit)	0.0	0.1	0.1
Amortization of net actuarial gain/(loss)	1.8	3.0	1.8
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements	0.0	0.0	0.0
Curtailment	0.0	0.0	0.0
Net periodic benefit cost	1.2	3.3	3.2
Medical Plan [Member]
Service cost	0.0	0.0	0.0
Interest cost	0.0	0.0	1.8
Expected return on plan assets	0.0	0.0	(0.3)
Amortization of prior service cost/(credit)	(11.3)	(11.3)	(2.3)
Amortization of net actuarial gain/(loss)	(0.3)	(0.3)	0.0
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements	9.0	0.0	0.0
Curtailment	0.0	0.0	(4.3)
Net periodic benefit cost	$ (20.6)	$ (11.6)	$ (5.1)