Employee Retirement Plans (Contributions and Benefit Payments) (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Oct. 15, 2017	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, lump-sum payments						$ 71,300,000
Defined benefit plan, pension liabilities settled						90,100,000
Settlement loss on pension benefit plans					$ 0	6,500,000
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement loss on pension benefit plans		$ 0	$ 6,500,000		0	$ 6,500,000
Pension Plans, Defined Benefit [Member] | Non-qualified [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit payments on non-qualified pension plans					800,000
Pension Plans, Defined Benefit [Member] | Qualified [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions on qualified pension plans					$ 0
Subsequent Event [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, lump-sum payments	$ 8,400,000			$ 18,900,000