Other Income and Expense (Other Expense) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of other operating expense [Line Items]
Allowance for other receivables	[1]	$ 0	$ 52	$ 0
Loss On Sale And Disposal Of Assets		28	12	0
Water Rights Write-Off		19	6	10
Other		10	9	14
Other Expenses		$ 57	$ 79	$ 24

[1] During the fourth quarter of 2016, we recognized a full allowance on a non-trade receivable in the MCAC SBU as a result of payment delays and discussions with the counterparty. The allowance relates to certain reimbursements the Company was expecting in connection with a legal matter. Management believes the counterparty is obligated to pay and plans to continue to attempt to fully collect the non-trade receivable.