Derivative Instruments and Hedging Activities, Balance Sheet Presentation Related to Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Assets	$ 0
Fair Value Hedging [Member]
Derivatives, Fair Value [Line Items]
Fair Value Hedges, Net	0	0
Enogex [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Assets		0
Liabilities		0.5
Enogex [Member] | Designated as Hedging Instrument [Member] | Natural Gas [Member] | Fixed Swaps/Futures [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Assets		0
Liabilities		0.5
Enogex [Member] | Not Designated as Hedging Instrument [Member] | Natural Gas [Member] | Options [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Assets		5.5	[1]
Liabilities		5.5	[1]
Enogex [Member] | Not Designated as Hedging Instrument [Member] | Natural Gas [Member] | Fixed Swaps/Futures [Member] | Current PRM [Member]
Derivatives, Fair Value [Line Items]
Assets		0.1
Liabilities		0
Enogex [Member] | Not Designated as Hedging Instrument [Member] | Natural Gas [Member] | Fixed Swaps/Futures [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Assets		5.0
Liabilities		4.7
Enogex [Member] | Not Designated as Hedging Instrument [Member] | Natural Gas [Member] | Physical [Member] | Current PRM [Member]
Derivatives, Fair Value [Line Items]
Assets		0.4
Liabilities		0.3
Enogex [Member] | Not Designated as Hedging Instrument [Member] | Natural Gas [Member] | Physical [Member] | Noncurrent PRM [Member]
Derivatives, Fair Value [Line Items]
Assets		5.5
Liabilities		$ 5.0

[1] See Note 5 for a reconciliation of the Company's total derivatives fair value to the Company's Consolidated Balance Sheet at December 31, 2012.