Derivative Instruments, Hedging Activities and Fair Value Measurements, Nonrecurring Fair Value Measurements (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Asset Impairment Charges [Abstract]
Impairment of long-lived assets	$ 0.9	$ 0.4
NGL Pipelines & Services [Member]
Asset Impairment Charges [Abstract]
Impairment of long-lived assets	0.0	0.2
Crude Oil Pipelines & Services [Member]
Asset Impairment Charges [Abstract]
Impairment of long-lived assets	0.2	0.0
Natural Gas Pipelines & Services [Member]
Asset Impairment Charges [Abstract]
Impairment of long-lived assets	0.7	0.2
Petrochemical & Refined Products Services [Member]
Asset Impairment Charges [Abstract]
Impairment of long-lived assets	$ 0.0	$ 0.0