Derivative Instruments, Hedging Activities and Fair Value Measurements, Level 3 Recurring Valuation Techniques (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) $ / bbl $ / gal	Dec. 31, 2018 USD ($)
Asset commodity derivatives - Crude oil [Member] | Liability commodity derivatives - Crude oil [Member] | Level 3 [Member] | Measurement Input, Commodity Forward Price [Member] | Minimum [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Fair value inputs, forward commodity price (in dollars per unit) | $ / bbl	57.62
Asset commodity derivatives - Crude oil [Member] | Liability commodity derivatives - Crude oil [Member] | Level 3 [Member] | Measurement Input, Commodity Forward Price [Member] | Maximum [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Fair value inputs, forward commodity price (in dollars per unit) | $ / bbl	58.65
Asset commodity derivatives - Propane [Member] | Liability commodity derivatives - Propane [Member] | Level 3 [Member] | Measurement Input, Commodity Forward Price [Member] | Minimum [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Fair value inputs, forward commodity price (in dollars per unit) | $ / gal	0.56
Asset commodity derivatives - Propane [Member] | Liability commodity derivatives - Propane [Member] | Level 3 [Member] | Measurement Input, Commodity Forward Price [Member] | Maximum [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Fair value inputs, forward commodity price (in dollars per unit) | $ / gal	0.62
Asset commodity derivatives - Natural gasoline [Member] | Liability commodity derivatives - Natural gasoline [Member] | Level 3 [Member] | Measurement Input, Commodity Forward Price [Member] | Minimum [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Fair value inputs, forward commodity price (in dollars per unit) | $ / gal	1.11
Asset commodity derivatives - Natural gasoline [Member] | Liability commodity derivatives - Natural gasoline [Member] | Level 3 [Member] | Measurement Input, Commodity Forward Price [Member] | Maximum [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Fair value inputs, forward commodity price (in dollars per unit) | $ / gal	1.15
Asset Commodity derivatives - Ethane [Member] | Liability Commodity Derivatives - Ethane [Member] | Level 3 [Member] | Measurement Input, Commodity Forward Price [Member] | Minimum [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Fair value inputs, forward commodity price (in dollars per unit) | $ / gal	0.17
Asset Commodity derivatives - Ethane [Member] | Liability Commodity Derivatives - Ethane [Member] | Level 3 [Member] | Measurement Input, Commodity Forward Price [Member] | Maximum [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Fair value inputs, forward commodity price (in dollars per unit) | $ / gal	0.24
Asset commodity derivatives - Normal butane [Member] | Liability commodity derivatives - Normal butane [Member] | Level 3 [Member] | Measurement Input, Commodity Forward Price [Member] | Minimum [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Fair value inputs, forward commodity price (in dollars per unit) | $ / gal	0.62
Asset commodity derivatives - Normal butane [Member] | Liability commodity derivatives - Normal butane [Member] | Level 3 [Member] | Measurement Input, Commodity Forward Price [Member] | Maximum [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Fair value inputs, forward commodity price (in dollars per unit) | $ / gal	0.69
Fair Value, Measurements, Recurring [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Commodity asset derivatives	$ 202.3	$ 161.9
Commodity liability derivatives	137.0	162.4
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Commodity asset derivatives	1.1	1.3
Commodity liability derivatives	6.3	$ 7.2
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Commodity asset derivatives	1.1
Commodity liability derivatives	6.3
Fair Value, Measurements, Recurring [Member] | Liability commodity derivatives - Crude oil [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Commodity liability derivatives	0.3
Fair Value, Measurements, Recurring [Member] | Liability commodity derivatives - Propane [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Commodity liability derivatives	1.7
Fair Value, Measurements, Recurring [Member] | Liability commodity derivatives - Natural gasoline [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Commodity liability derivatives	1.9
Fair Value, Measurements, Recurring [Member] | Liability Commodity Derivatives - Ethane [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Commodity liability derivatives	1.5
Fair Value, Measurements, Recurring [Member] | Liability commodity derivatives - Normal butane [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Commodity liability derivatives	0.9
Fair Value, Measurements, Recurring [Member] | Asset commodity derivatives - Crude oil [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Commodity asset derivatives	0.2
Fair Value, Measurements, Recurring [Member] | Asset commodity derivatives - Propane [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Commodity asset derivatives	0.0
Fair Value, Measurements, Recurring [Member] | Asset commodity derivatives - Natural gasoline [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Commodity asset derivatives	0.0
Fair Value, Measurements, Recurring [Member] | Asset Commodity derivatives - Ethane [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Commodity asset derivatives	0.9
Fair Value, Measurements, Recurring [Member] | Asset commodity derivatives - Normal butane [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Commodity asset derivatives	$ 0.0