Contract Balances (Contract Balances) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Jan. 01, 2018
Revenue from Contract with Customer [Abstract]
Unbilled receivables - current & non-current	$ 176.1	$ 149.1
Contract liabilities - current	(649.1)	(605.5)
Deferred revenue - non-current	(30.8)	(31.8)
Net contract assets/(liabilities)	(503.8)	$ (488.2)
Change in unbilled receivables - current & non-current	27.0
Change in contract liabilities - current	(43.6)
Change in deferred revenue - non-current	1.0
Change in net contract assets/(liabilities)	$ (15.6)