Hedging Activities and Fair Value Measurements, Nonrecurring Fair Value Measurements (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
South Texas natural gas gathering and processing assets [Member]
Assets, Fair Value Disclosure [Abstract]
Assets, fair value	$ 21.3
Asset Impairment Charges [Abstract]
Impairment of long-lived assets held and used	125.7
Marine transportation business [Member]
Asset Impairment Charges [Abstract]
Impairment of long-lived assets held and used	$ 256.7
Marine transportation business [Member] | Measurement input, discount rate [Member]
Asset Impairment Charges [Abstract]
Long-lived asset, measurement input	0.093
Marine transportation business [Member] | Measurement input, growth rate [Member]
Asset Impairment Charges [Abstract]
Long-lived asset, measurement input	0.021
Petrochemical and Refined Products Services [Member] | Marine transportation business [Member]
Assets, Fair Value Disclosure [Abstract]
Assets, fair value	$ 410.0
Fair Value, Measurements, Nonrecurring [Member] | South Texas natural gas gathering and processing assets [Member]
Assets, Fair Value Disclosure [Abstract]
Assets, fair value	21.3	[1]
Fair Value, Measurements, Nonrecurring [Member] | Marine transportation business [Member]
Assets, Fair Value Disclosure [Abstract]
Assets, fair value	410.0	[1]
Fair Value, Measurements, Nonrecurring [Member] | Level 1 [Member] | South Texas natural gas gathering and processing assets [Member]
Assets, Fair Value Disclosure [Abstract]
Assets, fair value	0.0	[1]
Fair Value, Measurements, Nonrecurring [Member] | Level 1 [Member] | Marine transportation business [Member]
Assets, Fair Value Disclosure [Abstract]
Assets, fair value	0.0	[1]
Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member] | South Texas natural gas gathering and processing assets [Member]
Assets, Fair Value Disclosure [Abstract]
Assets, fair value	0.0	[1]
Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member] | Marine transportation business [Member]
Assets, Fair Value Disclosure [Abstract]
Assets, fair value	0.0	[1]
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | South Texas natural gas gathering and processing assets [Member]
Assets, Fair Value Disclosure [Abstract]
Assets, fair value	21.3	[1]
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Marine transportation business [Member]
Assets, Fair Value Disclosure [Abstract]
Assets, fair value	$ 410.0	[1]

[1] Our fair value estimates for these assets were based on an income approach (i.e., a discounted cash flow approach).