Income Taxes (Schedule of Unrecognized Tax Benefits and Consolidated Liability for Tax Contingencies) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Unrecognized tax benefits	$ 169	$ 158	$ 258	$ 227
Accrued interest and penalties	23	14
Tax credits and other indirect benefits	(6)	(3)
Liability for tax contingencies	$ 186	$ 169