Income Taxes (Schedule of Unrecognized Tax Benefits and Liability for Contingent Income Taxes, Interest and Penalties) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Unrecognized tax benefits	$ 79	$ 88	$ 123	$ 114
Accrued interest and penalties	15	28	40
Tax credits and other indirect benefits	(31)	(40)	(54)
Liability for tax contingencies	$ 63	$ 76	$ 109