Description of Business and Accounting Policies - Other Income (Expense), Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Foreign currency gains (losses)	$ 247	$ 21	$ (266)
Marketable securities realized gains (losses)	(7)	(8)	(5)
Equity Warrant
Derivative [Line Items]
Derivative gains (losses)	$ 109	$ 67	$ 0