Financial Instruments Narrative (Details) bbl in Millions, $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2019 USD ($) bbl	Dec. 31, 2018 USD ($) bbl
Investment Segment
Derivative [Line Items]
Fair value derivative instruments with credit risk related contingent features in a liability position \| $	$ 0	$ 0
Not designated as hedging instrument \| Commodity contracts not considered probable of settlement [Member] \| Energy Segment
Derivative [Line Items]
Volume of derivatives (barrels) \| bbl	2	2

Fair value of credit risk derivative liability.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4K
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5708775-113959

Name:	us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant