Derivative Instruments (Effective Portion of Unrealized Gain (Loss)) (Details) - Derivatives in cash flow hedging relationships [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective portion of the unrealized gain (loss) recognized in Other Comprehensive Income for our derivative instruments designated as cash flow hedges contracts [Abstract]
Unrealized gain (loss) on derivative instruments recognized in Other Comprehensive Income, effective portion, net	$ 192	$ (176)	$ 150
Foreign currency contracts [Member]
Effective portion of the unrealized gain (loss) recognized in Other Comprehensive Income for our derivative instruments designated as cash flow hedges contracts [Abstract]
Unrealized gain (loss) on derivative instruments recognized in Other Comprehensive Income, effective portion, net	(402)	115	425
Cross-currency swap contracts [Member]
Effective portion of the unrealized gain (loss) recognized in Other Comprehensive Income for our derivative instruments designated as cash flow hedges contracts [Abstract]
Unrealized gain (loss) on derivative instruments recognized in Other Comprehensive Income, effective portion, net	581	(281)	(275)
Forward interest rate contract [Member]
Effective portion of the unrealized gain (loss) recognized in Other Comprehensive Income for our derivative instruments designated as cash flow hedges contracts [Abstract]
Unrealized gain (loss) on derivative instruments recognized in Other Comprehensive Income, effective portion, net	$ 13	$ (10)	$ 0