Commitments and Contingencies (Pace, Piedmont, Pasadena - Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2020	Mar. 31, 2020	Sep. 30, 2012	Sep. 30, 2008	Sep. 30, 2006
Pace, Florida
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 41,900,000				$ 42,000,000
Change in estimated exposure	0	$ 19,000,000
Pace, Florida | Discontinued Operations
Loss Contingencies [Line Items]
Pretax environmental expense		$ 19,000,000			$ 42,000,000
Piedmont, South Carolina
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	12,200,000			$ 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	$ 11,400,000
Total anticipated exposure			$ 13,000,000