Retirement and Deferred Compensation Plans - Schedule of Components of Net Periodic Benefit Cost and Other Amounts Recognized in Other Comprehensive Loss (Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension plans
Net Periodic Benefit Cost
Service cost	$ 15.1	$ 10.9	$ 10.1
Interest cost	12.7	11.6	10.6
Expected return on assets	(12.9)	(10.6)	(10.8)
Settlements	0.4
Net loss	1.2	1.4	0.9
Prior service cost	0.7	0.6	0.4
Net periodic benefit cost	17.2	13.9	11.2
Other Changes in Plan Assets and Benefit Obligation Recognized in Other Comprehensive Income/Loss
Net loss (gain)	45.5	(16.6)	(1.5)
Prior service cost	1.0	1.4	2.9
Amortization of net loss	(1.6)	(1.4)	(0.9)
Amortization of prior service cost	(0.7)	(0.6)	(0.4)
Total recognized in other comprehensive income/loss	44.2	(17.2)	0.1
Total recognized in net periodic benefit cost and other comprehensive income/loss	61.4	(3.3)	11.3
Retiree health care plan
Net Periodic Benefit Cost
Interest cost	0.5	0.5	0.6
Net loss		0.1	0.1
Prior service cost	(0.8)	(0.8)	(0.8)
Net periodic benefit cost	(0.3)	(0.2)	(0.1)
Other Changes in Plan Assets and Benefit Obligation Recognized in Other Comprehensive Income/Loss
Net loss (gain)	0.8	(0.5)	(0.3)
Amortization of net loss		(0.1)	(0.1)
Amortization of prior service cost	0.8	0.8	0.8
Total recognized in other comprehensive income/loss	1.6	$ 0.2	0.4
Total recognized in net periodic benefit cost and other comprehensive income/loss	$ 1.3		$ 0.3