Financial Instruments and Guarantees with Off-Balance-Sheet Risk (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 mW		Dec. 31, 2010	Dec. 31, 2009
Guarantee Obligations [Line Items]
Cash up front from sale of receivables	$ 3,462.7
Guarantor Obligations, Current Carrying Value	2,223.9
Financial Instruments and Guarantees with Off-Balance-Sheet Risk (Textuals) [Abstract]
Amount in bank guarantees, letters of credit and surety bonds related to collateral for surety companies, road maintenance, performance guarantees and other operations	242.2
Time Period Of Lease That Permits The Partnership To Purchase The Terminal	30 years
Maximum capacity of the securitization program	275.0
Amount available under the securitization program	41.7
Total consideration received by Company related to accounts receivable sold under securitization program	4,633.4
Additional cash upon collection of underlying receivables	1,004.8
Non collected receivables	165.9
Reduction in accounts receivable as a result of securitization	150.0		150.0
Expense associated with securitization transactions	2.0		2.4	4.0
Capacity of new electricity generation project, Megawatts	1,600
The Company's undivided interest percentage in the Prairie State Energy Campus	5.06%
Dominion Terminal Associates Partnership [Member]
Financial Instruments and Guarantees with Off-Balance-Sheet Risk (Textuals) [Abstract]
Equity Method Investment, Ownership Percentage	37.50%
Number of Letters of Credit Supporting Reimbursement Obligation	4
Maximum reimbursement obligation to commercial bank related to Dominion Terminals	42.7
Pension Plans Agreement With PBG and TXU Europe [Member]
Financial Instruments and Guarantees with Off-Balance-Sheet Risk (Textuals) [Abstract]
Letter of credit maintained by the Company in favor of the PBGC	37.0
Number of benefit pension plans	2
Guarantee in place from TXU Europe Limited	110.0
Reclamation Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	1,721.2
Lease Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	104.7
Workers' Compensation Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	76.1
Guarantee Type, Other [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	321.9	[1]
Self bonding [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	929.6
Self bonding [Member] | Reclamation Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	929.6
Self bonding [Member] | Lease Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	0
Self bonding [Member] | Workers' Compensation Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	0
Self bonding [Member] | Guarantee Type, Other [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	0	[1]
Surety bonds [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	742.4
Surety bonds [Member] | Reclamation Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	613.2
Surety bonds [Member] | Lease Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	104.7
Surety bonds [Member] | Workers' Compensation Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	13.5
Surety bonds [Member] | Guarantee Type, Other [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	11.0	[1]
Bank guarantees [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	389.6
Bank guarantees [Member] | Reclamation Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	178.4
Bank guarantees [Member] | Lease Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	0
Bank guarantees [Member] | Workers' Compensation Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	0
Bank guarantees [Member] | Guarantee Type, Other [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	211.2	[1]
Letters of credit [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	82.6
Letters of credit [Member] | Reclamation Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	0
Letters of credit [Member] | Lease Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	0
Letters of credit [Member] | Workers' Compensation Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	62.6
Letters of credit [Member] | Guarantee Type, Other [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	20.0	[1]
Bilateral cash collateralization agreements [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	79.7
Bilateral cash collateralization agreements [Member] | Reclamation Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	0
Bilateral cash collateralization agreements [Member] | Lease Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	0
Bilateral cash collateralization agreements [Member] | Workers' Compensation Obligations [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	0
Bilateral cash collateralization agreements [Member] | Guarantee Type, Other [Member]
Guarantee Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	$ 79.7	[1]

[1] Other includes bilateral cash collateralization agreement obligations described below and an additional $242.2 million in bank guarantees, letters of credit and surety bonds related to collateral for surety companies, road maintenance, performance guarantees and other operations.