Regulatory Accounting (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Unrecognized Equity Return	$ 363		$ 363
Amount Of Allowed Equity Return Recognized In Period	$ 17	$ 12	$ 30	$ 21