Property, Plant and Equipment Property, Plant and Equipment Class and Useful Life (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total PPE	$ 12,488.1	$ 12,148.3
Less:  accumulated depreciation	3,947.0	3,598.5
Total PPE, net	8,541.1	8,549.8
Depreciation expense for PPE	364.4	356.9	$ 344.2
Depreciable plant:
Property, Plant and Equipment [Line Items]
Total PPE	$ 12,051.1	$ 11,767.5
Weighted-Average Useful Lives (Years)	37 years	37 years
Depreciable plant: | Transmission
Property, Plant and Equipment [Line Items]
Total PPE	$ 10,672.7	$ 10,417.9
Weighted-Average Useful Lives (Years)	37 years	37 years
Depreciable plant: | Storage
Property, Plant and Equipment [Line Items]
Total PPE	$ 886.5	$ 863.5
Weighted-Average Useful Lives (Years)	38 years	38 years
Depreciable plant: | Gathering
Property, Plant and Equipment [Line Items]
Total PPE	$ 109.6	$ 108.0
Weighted-Average Useful Lives (Years)	23 years	23 years
Depreciable plant: | General
Property, Plant and Equipment [Line Items]
Total PPE	$ 228.6	$ 224.9
Weighted-Average Useful Lives (Years)	15 years	14 years
Depreciable plant: | Rights of way and other
Property, Plant and Equipment [Line Items]
Total PPE	$ 153.7	$ 153.2
Weighted-Average Useful Lives (Years)	33 years	33 years
Non-depreciable:
Property, Plant and Equipment [Line Items]
Total PPE	$ 437.0	$ 380.8
Non-depreciable: | Construction work in progress
Property, Plant and Equipment [Line Items]
Total PPE	239.5	184.2
Non-depreciable: | Storage
Property, Plant and Equipment [Line Items]
Total PPE	152.3	152.3
Non-depreciable: | Land
Property, Plant and Equipment [Line Items]
Total PPE	$ 45.2	$ 44.3