Other Income and Expense - Other Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Schedule of Other Nonoperating Income [Line Items]
Other income	$ 18	$ 12	$ 43	$ 42
Other Income [Member]
Schedule of Other Nonoperating Income [Line Items]
Public Utilities, Allowance for Funds Used During Construction, Additions	8	5	22	12
Gain On Sale Of Assets	0	1	3	12
Other Nonoperating Income	$ 10	$ 6	$ 18	$ 18