Derivative and Financial Instruments - Commodity Notional (Details) - Commodity Contract [Member] - USD ($) $ in Millions	Mar. 31, 2018	Dec. 01, 2017
Natural gas and power, Fixed price [Member] \| Short [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Commodity derivatives - volumetric material net exposures	12	29
Natural gas and power, Basis [Member] \| Long [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Commodity derivatives - volumetric material net exposures	2	12

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

Name:	invest_DerivativeNonmonetaryNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant