Retirement Benefit Plans (Reconciliation of beginning and ending fair value balances for assets with unobservable fair value inputs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Beginning balance	$ 423.2
Ending balance	424.1	$ 423.2
Significant Unobservable Inputs (Level 3) [Member]
Beginning balance	11.7	13.1
Unrealized gains/(losses) relating to the instrument still held at the reporting date	0.6	0.1
Purchases, sales, issuances and settlements (net)	(1.9)	(1.5)
Ending balance	$ 10.4	$ 11.7