Risk Management Energy Commodity Price Risk Management (Details) - Energy commodity derivative contracts(a)	Sep. 30, 2016 Bcf MMBbls
Crude oil fixed price | Derivatives designated as hedging contracts
Derivative [Line Items]
Derivative, Net Nonmonetary Notional Amounts | MMBbls	(19.4)
Crude oil fixed price | Derivatives not designated as hedging contracts
Derivative [Line Items]
Derivative, Net Nonmonetary Notional Amounts | MMBbls	(0.1)
Crude oil basis | Derivatives designated as hedging contracts
Derivative [Line Items]
Derivative, Net Nonmonetary Notional Amounts | MMBbls	(2.2)
Natural gas fixed price | Derivatives designated as hedging contracts
Derivative [Line Items]
Derivative, Net Nonmonetary Notional Amounts | Bcf	(27.5)
Natural gas fixed price | Derivatives not designated as hedging contracts
Derivative [Line Items]
Derivative, Net Nonmonetary Notional Amounts | Bcf	(9.9)
Natural gas basis | Derivatives designated as hedging contracts
Derivative [Line Items]
Derivative, Net Nonmonetary Notional Amounts | Bcf	(12.8)
Natural gas basis | Derivatives not designated as hedging contracts
Derivative [Line Items]
Derivative, Net Nonmonetary Notional Amounts | Bcf	(3.3)
Natural Gas Liquids Fixed Price [Member] | Derivatives not designated as hedging contracts
Derivative [Line Items]
Derivative, Net Nonmonetary Notional Amounts | MMBbls	(2.6)