Related Party Transactions (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Service Company [Member]
Related Party Transaction [Line Items]
Costs incurred by related party	$ 13.5	$ 12.2
Prepaid balance to related party	3.2		$ 1.2
Director [Member]
Related Party Transaction [Line Items]
Billings from related vendor	169.9	91.1
Accounts payable to related vendor	11.1		$ 34.0
Ipalco Enterprises, Inc. [Member]
Related Party Transaction [Line Items]
Costs incurred by related party	$ 4.1	$ 3.7