Employee Benefit Plans and Other Postretirement Benefits (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Apr. 30, 2016	Dec. 31, 2015
Pension Contributions [Abstract]
Increase in accumulated other comprehensive income (loss)	$ (114,200,000)		$ (114,200,000)			$ (124,900,000)
Postretirement Health Coverage | Adjustment
Pension Contributions [Abstract]
Decrease in benefit obligation					$ 5,100,000
Increase in accumulated other comprehensive income (loss)					3,100,000
Increase in deferred income taxes					$ 2,000,000
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	6,200,000	$ 6,100,000	18,400,000	$ 17,900,000
Interest cost	10,200,000	11,600,000	30,600,000	34,600,000
Expected return on plan assets	(12,300,000)	(13,300,000)	(37,100,000)	(39,800,000)
Net amortization of unrecognized amounts, Prior service cost	1,400,000	1,400,000	4,300,000	4,200,000
Net amortization of unrecognized amounts, Actuarial loss	1,500,000	2,100,000	4,300,000	6,400,000
Net periodic benefit cost	7,000,000	7,900,000	20,500,000	23,300,000
Pension Contributions [Abstract]
Contributions to pension plan	49,700,000	0	53,000,000	0
Minimum pension contributions			27,000,000
Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	100,000	400,000	500,000	1,300,000
Interest cost	100,000	300,000	500,000	900,000
Net amortization of unrecognized amounts, Prior service cost	(100,000)	0	(100,000)	0
Net amortization of unrecognized amounts, Actuarial loss	0	0	(400,000)	100,000
Net periodic benefit cost	$ 100,000	$ 700,000	$ 500,000	$ 2,300,000