Nonutility Real Estate & Other Legacy Holdings (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Investments by type [Abstract]
Other nonutility investments	$ 29.6	$ 40.9
Investments in Unconsolidated Affiliates	92.9	135.2
Haddington Energy Partnerships [Abstract]
Equity in earnings (losses) of unconsolidated affiliates	(32.0)	(8.6)	3.4
Other assets	40.3	33.7
Liabilities	1,160.3	1,069.4
Notes Receivable
Other nonutility investments identified above	29.6	40.9
Variable Interest Expense
Investments in Unconsolidated Affiliates	92.9	135.2
Other nonutility investments	29.6	40.9
Nonutility Group [Member]
Investments by type [Abstract]
Total carrying value by type of investment	36.9	52.7
Other nonutility investments	29.6
Investments in Unconsolidated Affiliates	7.3
Carrying value of legacy investments less deferred taxes of leveraged leases	23.1
Notes Receivable
Notes receivable	2.1	10.9
Accrued interest and reserves associated with notes receivable	15.7	6.1
Other nonutility investments identified above	29.6
Variable Interest Expense
Investments in Unconsolidated Affiliates	7.3
Other nonutility investments	29.6
Nonutility Group [Member] | Leveraged Leases Member
Investments by type [Abstract]
Total carrying value by type of investment	18.5
Other nonutility investments	18.5
Investments in Unconsolidated Affiliates	0
Leveraged Leases
Total equipment and facilities cost	45.2
Rentals due under the leases and a security interest in the leased property	39.8
Book value of divested leveraged lease	5.2
Net Book Value Of Deferred Taxes Of Divested Leveraged Lease	2.7
Notes Receivable
Other nonutility investments identified above	18.5
Variable Interest Expense
Investments in Unconsolidated Affiliates	0
Other nonutility investments	18.5
Nonutility Group [Member] | Commercial Real Estate Investments [Member]
Investments by type [Abstract]
Total carrying value by type of investment	8.0
Other nonutility investments	8.0
Investments in Unconsolidated Affiliates	0
Haddington Energy Partnerships [Abstract]
Equity in earnings (losses) of unconsolidated affiliates	3.6
Notes Receivable
Other nonutility investments identified above	8.0
Commercial real estate
Impairment charge	15.4
Amount of impairment charge included in Other-net	8.8
Other operating expenses	3.0
Variable Interest Expense
Investments in Unconsolidated Affiliates	0
Other nonutility investments	8.0
Nonutility Group [Member] | Affordable Housing Projects [Member]
Investments by type [Abstract]
Total carrying value by type of investment	3.1
Other nonutility investments	0.1
Investments in Unconsolidated Affiliates	3.0
Notes Receivable
Other nonutility investments identified above	0.1
Variable Interest Expense
Investments in Unconsolidated Affiliates	3.0
Other nonutility investments	0.1
Nonutility Group [Member] | Haddington Energy Partnerships [Member]
Investments by type [Abstract]
Total carrying value by type of investment	3.4
Other nonutility investments	0
Investments in Unconsolidated Affiliates	3.4
Haddington Energy Partnerships [Abstract]
Percentage of ownership interest in both Haddington Ventures (in hundredths)	40.00%
Number of remaining mid-stream energy related investments	2
Charge related to decline in fair value and note receivable impairment		6.5
Equity in earnings (losses) of unconsolidated affiliates		6.1
Amount charged to other income-net		0.4
Revenues		0	0
Operating income (loss)		(0.3)	(0.4)
Net income		(18.1)	7.9
Notes Receivable
Other nonutility investments identified above	0
Variable Interest Expense
Investments in Unconsolidated Affiliates	3.4
Other nonutility investments	0
Nonutility Group [Member] | Other Investments [Member]
Investments by type [Abstract]
Total carrying value by type of investment	3.9
Other nonutility investments	3.0
Investments in Unconsolidated Affiliates	0.9
Notes Receivable
Other nonutility investments identified above	3.0
Variable Interest Expense
Investments in Unconsolidated Affiliates	0.9
Other nonutility investments	3.0
Nonutility Group [Member] | Variable Interest Entities [Member]
Investments by type [Abstract]
Other nonutility investments	0.1	9.0
Investments in Unconsolidated Affiliates	3.0	7.0
Notes Receivable
Other nonutility investments identified above	0.1	9.0
Variable Interest Expense
Investments in Unconsolidated Affiliates	3.0	7.0
Other nonutility investments	$ 0.1	$ 9.0