Derivative Instruments, Hedging Activities and Fair Value Measurements, Nonrecurring Fair Value Measurements (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Asset Impairment Charges [Abstract]
Impairment of other current assets			$ 0.1	$ 11.7
Impairment of long-lived assets	$ 15.8	$ 13.1	16.7	13.5
NGL Pipelines & Services [Member]
Asset Impairment Charges [Abstract]
Impairment of long-lived assets	12.4	2.8	12.4	3.0
Crude Oil Pipelines & Services [Member]
Asset Impairment Charges [Abstract]
Impairment of long-lived assets	0.1	0.6	0.3	0.6
Natural Gas Pipelines & Services [Member]
Asset Impairment Charges [Abstract]
Impairment of long-lived assets	1.8	9.7	2.5	9.9
Petrochemical & Refined Products Services [Member]
Asset Impairment Charges [Abstract]
Impairment of long-lived assets	$ 1.5	$ 0.0	$ 1.5	$ 0.0