Commitments and Contingencies - Narrative (Details) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended											3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 25, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 North Attleboro Site [Member]	Dec. 31, 2012 Attorney General of Commonwealth [Member]	Dec. 31, 2012 Jal 4 Facility [Member]	Dec. 31, 2012 Jal 3 Facility [Member]	Dec. 31, 2012 Mercury Release [Member]	Sep. 30, 2012 Mercury Release [Member]	Dec. 31, 2009 Mercury Release [Member]	Dec. 31, 2012 Accrued Liabilities [Member]	Dec. 31, 2011 Accrued Liabilities [Member]	Mar. 25, 2012 Missouri Safety Program [Member]	Dec. 31, 2012 Missouri Safety Program [Member]	Dec. 31, 2011 Missouri Safety Program [Member]	Dec. 31, 2010 Missouri Safety Program [Member]
Commitments And Contingencies [Line Items]
Estimated remediation costs to completion					$ 11,000,000
Payments for Environmental Liabilities	1,000,000	3,000,000	3,000,000	4,000,000
Legal fees						19,000,000
Level of recovery						50.00%
Reimbursed expert and consultant costs, maximum						150,000
Alleged regulatory violations							1,000,000	7,000,000
Estimated cost											6,000,000
Community Service Obligation											12,000,000
Original Fine Amount										50,000
Fine Amount Sought										500,000
Accrued liabilities, litigation and other claim-related									1,000,000			27,000,000	28,000,000
Hurricane related expenses				141,000,000
Insurance Recoveries				65,000,000
Recorded Unconditional Purchase Obligation		181,000,000
Payments to Acquire Productive Assets														3,000,000	9,000,000	14,000,000	14,000,000
Estimated Future Capital Expenditures																	$ 135,000,000
Capital Expenditure Years																	10
Percentage Service Lines																	34.00%