Employee Benefit Plans and Other Postretirement Benefits - Change in Benefit Obligations and Change in Fair Value of Plan Assets Related to Pension and Postretirement Plans (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amounts Recognized on Consolidated Balance Sheets
Noncurrent liabilities		$ (357.5)	$ (372.5)
Pension Plans
Change in Benefit Obligations [Roll Forward]
Benefit obligation at beginning of period		1,300.2	1,158.4
Service cost		25.0	23.7	$ 24.5
Interest cost		42.4	41.6	40.9
Plan amendments		3.0	17.3
Actuarial (gain) loss	[1]	(121.1)	99.3
Participant contributions
Benefits paid		(44.6)	(40.1)
Benefit obligation at plan year end		1,204.9	1,300.2	1,158.4
Accumulated benefit obligation portion of above		1,163.3	1,237.7
Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at fair value at beginning of period		954.8	830.4
Actual return on plan assets		(59.9)	121.0
Company contributions		22.9	43.5
Benefits paid		(44.6)	(40.1)
Fair value of plan assets at plan year end		873.2	954.8	830.4
Underfunded status		(331.7)	(345.4)
Amounts Recognized on Consolidated Balance Sheets
Current liabilities		(1.4)	(1.4)
Noncurrent liabilities		(330.3)	(344.0)
Accrued obligation recognized at December 31		(331.7)	(345.4)
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)
Prior service cost (credit)		28.7	32.7
Actuarial loss (gain)		194.6	208.5
Total		223.3	241.2
Postretirement Plans
Change in Benefit Obligations [Roll Forward]
Benefit obligation at beginning of period		16.5	19.5
Service cost		0.3	0.3	0.5
Interest cost		0.5	0.6	0.6
Plan amendments		(0.4)	(0.5)
Actuarial (gain) loss	[1]	(1.2)	(2.2)
Participant contributions		1.1	1.3
Benefits paid		(2.2)	(2.5)
Benefit obligation at plan year end		14.6	16.5	$ 19.5
Change in Fair Value of Plan Assets [Roll Forward]
Company contributions		1.1	1.2
Participant contributions		1.1	1.3
Benefits paid		(2.2)	(2.5)
Underfunded status		(14.6)	(16.5)
Amounts Recognized on Consolidated Balance Sheets
Current liabilities		(0.8)	(1.0)
Noncurrent liabilities		(13.8)	(15.5)
Accrued obligation recognized at December 31		(14.6)	(16.5)
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)
Prior service cost (credit)		(5.4)	(5.3)
Actuarial loss (gain)		(5.0)	(4.0)
Total		$ (10.4)	$ (9.3)

[1] The actuarial gain in 2018 was due primarily to an increase in the weighted average discount rate used to estimate pension benefit obligations. The actuarial loss in 2017 was due primarily to a decrease in the weighted average discount rate used to estimate our pension benefit obligations.