Operations and Significant Accounting Policies - Reclassification of Prior Income Statement (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2016
Operating Revenue to Operating Revenue – Utility [Member]
Reclassification of Prior Income Statement [Line Items]
Prior Period Reclassification Amount	$ 234.9	$ 487.2
Operating Revenue to Operating Revenue – Non-utility [Member]
Reclassification of Prior Income Statement [Line Items]
Prior Period Reclassification Amount	79.9	161.4
Cost of Sales – Non-utility to Fuel, Purchased Power and Gas – Utility [Member]
Reclassification of Prior Income Statement [Line Items]
Prior Period Reclassification Amount	$ 0.9	$ 3.9