Organization and Basis of Presentation (Summarized Income Statement Data) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Operating Revenues	$ 883	$ 756	$ 767
Operating Expenses	622	561	526
Net Income	$ 365	$ 254	$ 225