Income Taxes (Schedule of Unrecognized Tax Benefits and Consolidated Liability for Tax Contingencies) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized tax benefits	$ 85	$ 66	$ 169	$ 158
Accrued interest and penalties	13	9
Tax credits and other indirect benefits	(1)	(1)
Liability for tax contingencies	$ 97	$ 74