Savings, Pension and Other Postretirement Employee Benefit Plans - Changes in Benefit Obligation, Plan Assets and Funded Status for Company-Sponsored Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Noncurrent assets	$ 0.0
Current liability for pension and other postretirement employee benefits	(7.4)	$ (7.4)
Liability for pension and other postretirement employee benefits	(76.6)	(78.2)
Liability, Defined Benefit Pension Plan	(9.9)	(25.4)
Liability, Other Postretirement Defined Benefit Plan	(66.4)	(60.3)
Pension Benefit Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	294.2	317.8
Service cost	2.4	1.8	$ 2.1
Interest cost	12.4	12.0	13.1
Actuarial losses (gains)	29.0	(16.3)
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(21.5)	(21.1)
Benefit obligation at end of year	316.5	294.2	317.8
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	268.8	310.9
Actual return on plan assets	58.8	(21.5)
Employer contribution	0.5	0.5
Defined Benefit Plan, Plan Assets, Benefits Paid	21.5	21.1
Fair value of plan assets at end of year	306.6	268.8	310.9
Funded status at end of year	(9.9)	(25.4)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Noncurrent assets	7.7	0.0
Current liability for pension and other postretirement employee benefits	(0.4)	(0.4)
Liability for pension and other postretirement employee benefits	(17.2)	(25.0)
Net actuarial loss (gain)	91.4	111.9
Other Postretirement Employee Benefit Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	60.3	65.1
Service cost	0.1	0.1	0.2
Interest cost	2.8	2.4	2.7
Actuarial losses (gains)	9.6	(0.3)
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(6.4)	(7.0)
Benefit obligation at end of year	66.4	60.3	65.1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0.0	0.0
Actual return on plan assets	0.0	0.0
Employer contribution	7.0	7.0
Defined Benefit Plan, Plan Assets, Benefits Paid	7.0	7.0
Fair value of plan assets at end of year	0.0	0.0	$ 0.0
Funded status at end of year	(66.4)	(60.3)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Noncurrent assets	0.0	0.0
Current liability for pension and other postretirement employee benefits	(7.0)	(7.0)
Liability for pension and other postretirement employee benefits	(59.4)	(53.3)
Net actuarial loss (gain)	$ (5.1)	$ (15.0)