Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2012

Fair Value Measurements [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]

						Fair Value Measurements Using
							Quoted
							Prices In
							Active		Significant
							Markets for		Other		Significant
							Identical		Observable		Unobservable
		Carrying		Fair			Assets		Inputs		Inputs
		Amount		Value			(Level 1)		(Level 2)		(Level 3)
		(Millions)
Assets (liabilities) at December 31, 2012:
	Measured on a recurring basis:
	ARO Trust investments	$	17.8	$	17.8		$	17.8	$	-	$	-
	Additional disclosures:
	Notes receivable		8.2		8.2			-		8.2		-
	Long-term debt		(1,428.3)		(1,704.5)			-		(1,704.5)		-
Assets (liabilities) at December 31, 2011:
	Measured on a recurring basis:
	ARO Trust investments	$	24.5	$	24.5		$	24.5	$	-	$	-
	Additional disclosures:
	Notes receivable		9.5		9.5			N/A		N/A		N/A
	Long-term debt, including current portion		(1,353.7)		(1,539.2)			N/A		N/A		N/A