Regulatory Accounting (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Unrecognized Equity Return	$ 341		$ 341
Amount Of Allowed Equity Return Recognized In Period	$ 22	$ 16	$ 52	$ 37