Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012
Related Party Transaction [Line Items]
Dividends declared on common stock					$ 120.0		$ 75.0
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	28.7		28.8		87.2		89.0
Og and E [Member] | Enogex [Member]
Related Party Transaction [Line Items]
Electricity to power electric compression assets	3.9		4.6		7.8		10.3
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		26.1		26.1
Og and E [Member] | Natural Gas Storage [Member] | Enogex [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	3.2		3.2		9.7		9.6
Og and E [Member] | Natural Gas Purchases [Member] | Enogex [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	9.5	[1]	8.7	[1]	19.5	[1]	18.3	[1]
Related Party Transaction, Due from (to) Related Party	$ 1.4				$ 1.4				$ 1.0

[1] At September 30, 2013 and December 31, 2012, respectively, there were $1.4 million and $1.0 million of natural gas purchases recorded for these activities.