Commitments and Contingencies (Pace, Piedmont, Pasadena Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2012	Sep. 30, 2008	Sep. 30, 2006
Pace, Florida
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 28,500,000			$ 42,000,000
Change in estimated exposure	0
Pace, Florida | Discontinued Operations
Loss Contingencies [Line Items]
Pretax environmental expense				42,000,000
Pace, Florida | Minimum
Loss Contingencies [Line Items]
Estimate of possible exposure from environmental loss contingencies				42,000,000
Pace, Florida | Maximum
Loss Contingencies [Line Items]
Estimate of possible exposure from environmental loss contingencies				$ 52,000,000
Piedmont, South Carolina
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	16,400,000		$ 24,000,000
Piedmont, South Carolina | Discontinued Operations
Loss Contingencies [Line Items]
Pretax environmental expense			$ 24,000,000
Pasadena, Texas
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 12,000,000.0
Total anticipated exposure		$ 13,000,000