Property, Plant, and Equipment - Balances (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Property, plant, and equipment
Accumulated depreciation	$ 8,515.9	$ 8,618.5
Net property, plant, and equipment	22,000.9	21,347.0
Utility operations
Property, plant, and equipment
Accumulated depreciation	7,573.6	7,021.8
Net	17,961.8	17,555.5
CWIP	707.5	508.2
Net property, plant, and equipment	18,669.3	18,063.7
Utility operations | Electric - generation
Property, plant, and equipment
Property, plant, and equipment	6,410.6	6,071.8
Utility operations | Electric - distribution
Property, plant, and equipment
Property, plant, and equipment	6,534.6	6,137.5
Utility operations | Natural gas - distribution, storage, and transmission
Property, plant, and equipment
Property, plant, and equipment	10,766.3	10,055.9
Utility operations | Property, plant, and equipment to be retired, net
Property, plant, and equipment
Property, plant, and equipment to be retired, net	174.8	930.6
Utility operations | Other
Property, plant, and equipment
Property, plant, and equipment	1,649.1	1,381.5
Non-utility operations
Property, plant, and equipment
Accumulated depreciation	731.5	671.3
Net	3,249.1	3,125.9
CWIP	82.5	157.4
Net property, plant, and equipment	3,331.6	3,283.3
Non-utility operations | Other
Property, plant, and equipment
Property, plant, and equipment	127.1	166.9
Non-utility operations | We Power generation
Property, plant, and equipment
Property, plant, and equipment	3,244.4	3,215.9
Non-utility operations | Renewable generation
Property, plant, and equipment
Property, plant, and equipment	193.3	0.0
Non-utility operations | Natural gas storage
Property, plant, and equipment
Property, plant, and equipment	244.8	244.8
Non-utility operations | Corporate services
Property, plant, and equipment
Property, plant, and equipment	171.0	169.6
Non-Utility Energy Infrastructure | Non-utility operations
Property, plant, and equipment
Property, plant, and equipment	$ 3,682.5	$ 3,460.7