Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012
Related Party Transaction [Line Items]
Dividends declared on common stock					$ 80.0		$ 0
Operating Costs Charged [Member] | Og and E [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party	28.1		27.5		58.5		60.2
Og and E [Member] | Enogex [Member]
Related Party Transaction [Line Items]
Revenue from Related Parties	2.1		2.9		3.9		5.7
Og and E [Member] | Natural Gas Transportation [Member] | Enogex [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	8.7		8.7		17.4		17.4
Og and E [Member] | Natural Gas Storage [Member] | Enogex [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	3.4		3.2		6.5		6.4
Og and E [Member] | Natural Gas Purchases [Member] | Enogex [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	4.5	[1]	6.0	[1]	10.0	[1]	9.6	[1]
Related Party Transaction, Due from (to) Related Party	$ 1.2				$ 1.2				$ 1.0

[1] At June 30, 2013 and December 31, 2012, respectively, there were $1.2 million and $1.0 million of natural gas purchases recorded for these activities.