Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan [Abstract]
Expenses relating to defined contribution plans	$ 42.4	$ 41.8	$ 36.7
Projected benefit plan obligations of Terra Nova Pension Plan	191.4	171.5
Fair value of Terra Nova Pension Plan assets	$ 216.9	$ 187.0