Other Income and Expense - Other Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule of other expense [Line Items]
Gain (Loss) on Disposition of Assets			$ (23)	$ (34)
Other Expenses	$ 29	$ 36	42	67
Other Expense [Member]
Schedule of other expense [Line Items]
Gain (Loss) on Disposition of Assets	20	5	25	26
Water Rights Write-Off	0	15	0	18
Allowance for other receivables	0	15	0	15
Other Nonoperating Expense	9	1	17	8
Other Expenses	$ 29	$ 36	$ 42	$ 67