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Financial Instruments Narrative (Details)
bbl in Millions, $ in Millions
9 Months Ended 12 Months Ended
Sep. 30, 2017
USD ($)
bbl
Dec. 31, 2016
USD ($)
bbl
Investment Segment    
Derivative [Line Items]    
Fair value derivative instruments with credit risk related contingent features in a liability position | $ $ 7 $ 39
Not designated as hedging instrument | Commodity contracts | Energy Segment    
Derivative [Line Items]    
Volume of derivatives (barrels) | bbl 16.2 4.0