Subsequent Events (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended	30 Months Ended	0 Months Ended	2 Months Ended
	Dec. 31, 2014	Aug. 22, 2017	Feb. 22, 2015 union Participant	Mar. 04, 2015
Subsequent Event [Line Items]
Change in deferred tax asset, offset by decrease in valuation allowance	$ 58.2
Qualified Pension | Represented Employees
Subsequent Event [Line Items]
Length of credited service cap	30 years
Qualified Pension | Represented Employees | Forecast
Subsequent Event [Line Items]
Retirement period for eligibility of medical insurance premium reimbursement		30 months
Subsequent Event
Subsequent Event [Line Items]
Number of labor unions			2
Number of participants			1,700
Subsequent Event | Qualified Pension | Represented Employees
Subsequent Event [Line Items]
Benefit accrual rate as percent of prior rate			50.00%
Length of credited service cap			30 years
Subsequent Event | Qualified Pension | Represented Employees | Forecast
Subsequent Event [Line Items]
Retirement period for eligibility of medical insurance premium reimbursement		30 months
Minimum | Qualified Pension
Subsequent Event [Line Items]
Change in deferred tax asset, offset by decrease in valuation allowance	30.0
Minimum | Subsequent Event | Qualified Pension
Subsequent Event [Line Items]
Esimated decrease in pension plan obligations				35
Minimum | Subsequent Event | Post-retirement Healthcare
Subsequent Event [Line Items]
Estimated decrease in postretirement obligations				620
Maximum | Post-retirement Healthcare
Subsequent Event [Line Items]
Change in deferred tax asset, offset by decrease in valuation allowance	40.0
Maximum | Subsequent Event | Qualified Pension
Subsequent Event [Line Items]
Esimated decrease in pension plan obligations				45
Maximum | Subsequent Event | Post-retirement Healthcare
Subsequent Event [Line Items]
Estimated decrease in postretirement obligations				$ 640