Derivative Instruments, Hedging Activities and Fair Value Measurements (Details) bbl in Millions, $ in Millions, ft³ in Billions		1 Months Ended	12 Months Ended
		Jan. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) Contract bbl ft³	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Derivative [Line Items]
Cash gain realized to due settlement of interest rate derivative instruments | $			$ 30.6	$ 6.1	$ 0.0
Interest Rate Swaps Hedging Senior Notes OO [Member] | Derivatives in fair value hedging relationships [Member]
Derivative [Line Items]
Number of Derivatives Outstanding | Contract			10
Type of Derivatives Outstanding			fixed-to-floating swaps
Notional Amount | $			$ 750.0
Derivative, Inception Date			May 01, 2015
Expected Termination Date			May 01, 2018
Rate Swap, fixed rate			1.65%
Rate Swap, floating rate			1.87%
Forward Starting Swaps [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Cash gain realized to due settlement of interest rate derivative instruments | $			$ 30.6	$ 6.1
Forward Starting Swaps [Member] | Derivatives in cash flow hedging relationships [Member] | Subsequent Event [Member]
Derivative [Line Items]
Notional amount of settled derivative instruments | $		$ 100.0
Cash gain realized to due settlement of interest rate derivative instruments | $		$ 1.5
Forward Starting Swaps B [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Number of Derivatives Outstanding | Contract			3
Type of Derivatives Outstanding			forward starting swaps
Notional Amount | $			$ 275.0
Expected Termination Date			Feb. 01, 2019
Average Rate Locked			2.57%
Designated as Hedging Instrument [Member] | Octane enhancement: Forecasted purchases of NGLs [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume	[1],[2]		1.1
Designated as Hedging Instrument [Member] | Octane enhancement: Forecasted sales of octane enhancement products [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume	[1],[2]		1.0
Designated as Hedging Instrument [Member] | Natural gas marketing: Forecasted purchases of natural gas for fuel [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume | ft³	[1],[2]		1.0
Designated as Hedging Instrument [Member] | Natural gas marketing: Natural gas storage inventory management activities [Member] | Derivatives in fair value hedging relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume | ft³	[1],[2]		3.9
Designated as Hedging Instrument [Member] | NGL marketing: Forecasted purchases of NGLs and related hydrocarbon products [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume	[1],[2]		49.0
Designated as Hedging Instrument [Member] | NGL marketing: Forecasted sales of NGLs and related hydrocarbon products [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume	[1],[2]		64.6
Designated as Hedging Instrument [Member] | NGL marketing: NGLs inventory management activities [Member] | Derivatives in fair value hedging relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume	[1],[2]		0.5
Designated as Hedging Instrument [Member] | Refined products marketing: Forecasted purchases of refined products [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume	[1],[2]		0.6
Designated as Hedging Instrument [Member] | Refined products marketing: Forecasted sales of refined products [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume	[1],[2]		1.3
Designated as Hedging Instrument [Member] | Refined products marketing: Refined products inventory management activities [Member] | Derivatives in fair value hedging relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume	[1],[2]		0.5
Designated as Hedging Instrument [Member] | Crude oil marketing: Forecasted purchases of crude oil [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume	[1],[2]		3.7
Derivative instruments, long-term volume	[1],[2]		3.3
Designated as Hedging Instrument [Member] | Crude oil marketing: Forecasted sales of crude oil [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume	[1],[2]		6.9
Derivative instruments, long-term volume	[1],[2]		3.3
Designated as Hedging Instrument [Member] | Petrochemical marketing: Forecasted purchases of NGLs for propylene marketing activities [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume	[1],[2]		0.8
Not Designated as Hedging Instrument [Member] | Natural gas risk management activities [Member] | Derivatives in mark-to-market relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume | ft³	[1],[2],[3],[4]		67.3
Derivative instruments, long-term volume | ft³	[1],[2],[3],[4]		9.0
Current natural gas hedging volumes designated as an index plus or minus a discount | ft³			21.1
Long-term natural gas hedging volumes designated as an index plus or minus a discount | ft³			5.3
Not Designated as Hedging Instrument [Member] | NGL risk management activities [Member] | Derivatives in mark-to-market relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume	[1],[2],[4]		18.3
Not Designated as Hedging Instrument [Member] | Refined products risk management activities [Member] | Derivatives in mark-to-market relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume	[1],[2],[4]		0.6
Not Designated as Hedging Instrument [Member] | Crude oil risk management activities [Member] | Derivatives in mark-to-market relationships [Member]
Derivative [Line Items]
Derivative instruments, current volume	[1],[2],[4]		104.0
Derivative instruments, long-term volume	[1],[2],[4]		12.2

[1] The maximum term for derivatives designated as cash flow hedges, derivatives designated as fair value hedges and derivatives not designated as hedging instruments is December 2020, May 2018 and December 2020, respectively.

[2] Volume for derivatives designated as hedging instruments reflects the total amount of volumes hedged whereas volume for derivatives not designated as hedging instruments reflects the absolute value of derivative notional volumes.

[3] Current and long-term volumes include 21.1 Bcf and 5.3 Bcf, respectively, of physical derivative instruments that are predominantly priced at a marked-based index plus a premium or minus a discount related to location differences.

[4] Reflects the use of derivative instruments to manage risks associated with transportation, processing and storage assets.