Property, Plant, and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 8,214.6	$ 7,919.1
Net property, plant, and equipment	19,915.5	19,189.7
Utility operations
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	24,185.1	22,803.7
Accumulated depreciation	7,609.7	7,358.2
Net	16,575.4	15,445.5
CWIP	320.0	672.7
Net property, plant, and equipment	16,895.4	16,118.2
Nonutility operations
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	3,520.3	3,482.2
Accumulated depreciation	604.9	560.9
Net	2,915.4	2,921.3
CWIP	104.7	150.2
Net property, plant, and equipment	$ 3,020.1	$ 3,071.5