Stockholders' Equity (Summary Of Dividends Paid On Common Stock) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017
Stockholders Equity Note [Abstract]
Common stock dividends paid, Amount	$ 42	$ 32	$ 33	$ 32	$ 74	$ 65
Common stock dividends, rate per share	$ 0.08	$ 0.06	$ 0.06	$ 0.06