Retirement Benefits - Fair Value Measurements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Net asset value per share practical expedient(a)	$ 37.2	$ 17.2
Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	215.1	180.6	$ 202.9
Non-U.S. Plans | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 177.9	$ 163.4