Risk Management Credit Risks (Details) - Energy Related Derivative - USD ($) $ in Millions |
Dec. 31, 2018 |
Dec. 31, 2017 |
---|---|---|
Credit Derivatives [Line Items] | ||
Letters of Credit Outstanding, Amount | $ 0 | |
Initial Margin Requirements | 9 | |
Variation Margin Requirements | 25 | |
Other Current Liabilities [Member] | Contract and Over the Counter | ||
Credit Derivatives [Line Items] | ||
Derivative, Collateral, Right to Reclaim Cash | $ 16 | |
Restricted Deposit [Member] | Contract and Over the Counter | ||
Credit Derivatives [Line Items] | ||
Derivative, Collateral, Right to Reclaim Cash | $ 1 |