Property Plant and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 21,815.4	$ 20,643.0
Accumulated depreciation and amortization	7,945.3	7,454.8
Property, Plant and Equipment, Net	14,244.0	13,541.7
Electric plant
Property, Plant and Equipment [Line Items]
Property, plant and equipment	18,519.5	17,749.3
Natural gas plant
Property, Plant and Equipment [Line Items]
Property, plant and equipment	1,562.9	1,475.5
Common and other property
Property, Plant and Equipment [Line Items]
Property, plant and equipment	886.7	803.1
CWIP
Property, Plant and Equipment [Line Items]
Property, plant and equipment	846.3	615.1
Nuclear fuel
Property, Plant and Equipment [Line Items]
Property, plant and equipment	2,909.8	2,770.4
Accumulated depreciation and amortization	$ 2,535.9	$ 2,416.9