Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Service Company [Member]
Related Party Transaction [Line Items]
Costs incurred by related party	$ 6.1	$ 4.4	$ 18.3	$ 18.0
Prepaid balance to related party	2.1		2.1		$ 0.4
Director [Member]
Related Party Transaction [Line Items]
Billings from related vendor	61.7	33.5	152.9	46.0
Accounts payable to related vendor	24.2		24.2		$ 11.9
Ipalco Enterprises, Inc. [Member]
Related Party Transaction [Line Items]
Costs incurred by related party	$ 1.9	$ 1.8	$ 5.6	$ 3.9