Commitment and Contingenices (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Contingent Residual Support Agreement, Amount	$ 2,000
Estimated litigation liability	21	$ 21
Accrued Environmental Loss Contingencies, Noncurrent	$ 2