CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement [Abstract]
Operating revenues	$ 638.3	$ 837.1	$ 1,801.8	$ 2,475.4
Cost of sales	217.1	400.2	790.2	1,373.1
Operating and maintenance expense	268.0	318.0	540.1	662.4
Depreciation and amortization expense	72.1	72.8	147.5	144.2
Property and revenue taxes	17.9	17.2	36.1	34.7
Merger costs	59.3	5.9	60.0	5.9
Impairment loss on property, plant, and equipment at PDL	10.7	0.0	10.7	0.0
Gain on sale of certain PDL solar power generation plants	(5.2)	0.0	(5.2)	0.0
Operating (loss) income	(1.6)	23.0	222.4	255.1
Equity in earnings of transmission affiliate	22.4	23.0	39.4	45.5
Miscellaneous income	1.8	5.8	9.1	12.3
Interest expense	40.0	39.3	79.0	79.0
Other expense	(15.8)	(10.5)	(30.5)	(21.2)
(Loss) income before taxes	(17.4)	12.5	191.9	233.9
(Benefit) provision for income taxes	(8.1)	4.5	70.9	86.4
Net (loss) income from continuing operations	(9.3)	8.0	121.0	147.5
Discontinued operations, net of tax	0.0	(0.8)	(0.8)	12.1
Net (loss) income	$ (9.3)	$ 7.2	$ 120.2	$ 159.6