Retirement and Deferred Compensation Plans - Changes in Fair Value of Pension Assets Measured Using Level 3 Inputs (Details) - Pension plans - Common contractual funds and insurance contracts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Change in Plan Assets
Fair value of plan assets, beginning of year	$ 108.8	$ 126.2
Transfers	46.2	(25.4)
Actual return on plan assets	4.2	(5.3)
Purchases, sales and settlements, net	(0.3)	(0.6)
Currency exchange rate changes	(5.0)	13.9
Fair value of plan assets, end of year	$ 153.9	$ 108.8