Employee Benefit Plans and Other Postretirement Benefits (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Apr. 30, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Increase in accumulated other comprehensive income (loss)	$ (116,900,000)		$ (116,900,000)			$ (124,900,000)
Postretirement Health Coverage | Adjustment
Defined Benefit Plan Disclosure [Line Items]
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	6,100,000	$ 6,000,000	12,200,000	$ 11,800,000
Interest cost	10,200,000	11,500,000	20,400,000	23,000,000
Expected return on plan assets	(12,400,000)	(13,300,000)	(24,800,000)	(26,600,000)
Net amortization of unrecognized amounts, Prior service cost	1,400,000	1,400,000	2,800,000	2,800,000
Net amortization of unrecognized amounts, Actuarial loss	1,400,000	2,200,000	2,800,000	4,300,000
Net periodic benefit cost	6,700,000	7,800,000	13,400,000	15,300,000
Pension Contributions [Abstract]
Contributions to pension plan	3,700,000		0	0
Expected contributions to pension plan			27,000,000
Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	200,000	400,000	400,000	800,000
Interest cost	200,000	300,000	400,000	600,000
Net amortization of unrecognized amounts, Prior service cost	0	0	0	0
Net amortization of unrecognized amounts, Actuarial loss	(200,000)	0	(400,000)	100,000
Net periodic benefit cost	$ 200,000	$ 700,000	$ 400,000	$ 1,500,000