- Amounts Recognized in Consolidated Balance Sheets (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 01, 2014	Dec. 31, 2013
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Noncurrent assets	$ 24.7		$ 26.5
Noncurrent liabilities	(29.6)		(20.2)
Regulatory asset		72.5
Regulatory liability		(28.5)
Pension Plans
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Noncurrent assets	0		0
Current liabilities	0		(6.1)
Noncurrent liabilities	(29.6)		(67.7)
Net benefit asset noncurrent	0		0
Net benefit liability noncurrent	(29.6)		(20.2)
Regulatory asset	67.8		58.5
Regulatory liability	(1.9)		0
Net asset (liability) recognized	(29.6)		(73.8)
Postretirement Plans
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Noncurrent assets	24.7		35.4
Current liabilities	0		0
Noncurrent liabilities	0		0
Net benefit asset noncurrent	24.7		26.5
Net benefit liability noncurrent	0		0
Regulatory asset	4.7		0
Regulatory liability	(26.6)		(26.2)
Net asset (liability) recognized	$ 24.7		$ 35.4