Other Income and Expense - Other Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of other expense [Line Items]
Gain (Loss) on Disposition of Assets			$ (2)	$ (19)
Other Expenses	$ 4	$ 7	13	31
Other Expense [Member]
Schedule of other expense [Line Items]
Gain (Loss) on Disposition of Assets	3	0	5	21
Water Rights Write-Off	0	3	0	3
Defined Benefit Plan, Other Cost (Credit)		(2)	1
Other Nonoperating Expense	1	4	8	7
Other Expenses	$ 4	$ 7	$ 13	$ 31