Derivatives and Risk Management Activities - Commodity Price Risk Hedging (Details) bbl in Millions, Mcf in Millions, MWh in Millions	3 Months Ended
	Mar. 31, 2017 MWh Mcf bbl
Net long position associated with crude oil purchases
Commodity Price Risk Hedging:
Derivative position notional amount (in barrels or Mcf)	2.6
Net short time spread position hedging anticipated crude oil lease gathering purchases
Commodity Price Risk Hedging:
Derivative position notional amount (in barrels or Mcf)	4.6
Crude oil grade basis position
Commodity Price Risk Hedging:
Derivative position notional amount (in barrels or Mcf)	42.1
Net short position related to anticipated sales of natural gas inventory
Commodity Price Risk Hedging:
Derivative position notional amount (in barrels or Mcf) | Mcf	3.5
Net short position related to anticipated net sales of crude oil and NGL inventory
Commodity Price Risk Hedging:
Derivative position notional amount (in barrels or Mcf)	24.0
PLA oil long call option position
Commodity Price Risk Hedging:
Derivative position notional amount (in barrels or Mcf)	0.8
Long natural gas position for natural gas purchases
Commodity Price Risk Hedging:
Derivative position notional amount (in barrels or Mcf) | Mcf	56.7
Short propane position related to subsequent sale of products
Commodity Price Risk Hedging:
Derivative position notional amount (in barrels or Mcf)	10.1
Short butane position related to subsequent sale of products
Commodity Price Risk Hedging:
Derivative position notional amount (in barrels or Mcf)	3.1
Short WTI position related to subsequent sale of products
Commodity Price Risk Hedging:
Derivative position notional amount (in barrels or Mcf)	1.0
Long power position for power supply requirements
Commodity Price Risk Hedging:
Derivative position notional amount (in megawatt hours) | MWh	0.4