Valuation And Qualifying Accounts [Schedule] Valuation And Qualifying Accounts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Reserve For Accounts Receivable [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	$ 30.5		$ 37.4		$ 39.6
Valuation Allowances and Reserves, Charged to Cost and Expense	13.2		13.8		17.6
Valuation Allowances and Reserves, Charged to Other Accounts	53.8	[1]	76.6	[1]	72.5	[1]
Deductions for Purposes for which Reserves were Created	73.5		97.3		92.3
Ending Balance	24.0		30.5		37.4
Reserve For Other Investments [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	3.0		3.0		3.0
Valuation Allowances and Reserves, Charged to Cost and Expense	0		0		0
Valuation Allowances and Reserves, Charged to Other Accounts	0	[1]	0	[1]	0	[1]
Deductions for Purposes for which Reserves were Created	0		0		0
Ending Balance	3.0		3.0		3.0
Reserve for Cost of Operational Gas [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	2.7		2.7		5.7
Valuation Allowances and Reserves, Charged to Cost and Expense	(1.5)		0		(2.9)
Valuation Allowances and Reserves, Charged to Other Accounts	0	[1]	0	[1]	0	[1]
Deductions for Purposes for which Reserves were Created	1.2		0		0.1
Ending Balance	$ 0		$ 2.7		$ 2.7

[1] Charged to Other Accounts reflects the deferral of bad debt expense to a regulatory asset.