Employee Benefits (Details) employee in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) employee	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Number of Fixed Income Funds Investing in Debt Securities Ecured by Royalty Payments [Line Items]
Number of employees sponsored by defined benefit pension plans | employee	9
Profit sharing bonus			$ 0
Employer discretionary contribution amount	$ 13,300,000	$ 10,300,000	7,200,000
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	1,228,400,000	1,233,600,000
Service cost	0	5,400,000
Interest cost	44,100,000	51,100,000
Benefits paid	(110,400,000)	(108,000,000)
Actuarial loss	(88,500,000)	63,500,000
Expenses paid from assets	0	(6,900,000)
Plan amendments	0	(10,700,000)
Other	(400,000)	400,000
Benefit obligation at year end	1,073,200,000	1,228,400,000	1,233,600,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets beginning of year	998,300,000	878,700,000
Actual return on plan assets	(27,800,000)	166,100,000
Employer contributions	15,200,000	68,000,000
Benefits paid	110,400,000	108,000,000
Expenses paid from assets	0	(6,900,000)
Other	(400,000)	400,000
Fair value of plan assets at year end	874,900,000	998,300,000	878,700,000
Funded status at year end	(198,300,000)	(230,100,000)
Noncurrent assets	2,700,000	3,300,000
Current liabilities	800,000	800,000
Noncurrent liabilities	200,200,000	232,600,000
Net actuarial loss	368,900,000	395,300,000
Net prior service credit	(10,300,000)	(10,700,000)
Unrecognized actuarial losses before tax	358,600,000	384,600,000
Unrecognized actuarial losses net of tax	334,400,000
Actuarial loss included in accumulated other comprehensive income and expected to be recognized next year	11,900,000
Expected amortization of prior service credit next fiscal year	(400,000)
Other Postretirement Benefits Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost	0	5,400,000	6,500,000
Interest cost	44,100,000	51,100,000	55,900,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Settlement adjustment	$ 10,900,000	$ 7,600,000	$ 0