Financial Instruments (Schedule of Cash, Cash Equivalents and Marketable Securities) (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended
		Sep. 30, 2016	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Cash and Cash Equivalents [Line Items]
Cash		$ 1,839	$ 1,839	$ 1,938
Cash and cash equivalents		4,452	4,452	5,300	$ 3,324	$ 6,910
Marketable securities		1,080	1,080	906
Proceeds from sale of available-for-sale securities		161	626
Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Cash		1,839	1,839	1,938
Marketable Securities [Member]
Cash and Cash Equivalents [Line Items]
Cash		0	0	0
Fair Value, Inputs, Level 1 [Member]
Cash and Cash Equivalents [Line Items]
Money market funds		0	0	550
U.S. Treasury securities	[1]	161	161	788
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Money market funds		0	0	550
U.S. Treasury securities	[1]	0	0	0
Fair Value, Inputs, Level 1 [Member] | Marketable Securities [Member]
Cash and Cash Equivalents [Line Items]
Money market funds		0	0	0
U.S. Treasury securities	[1]	161	161	788
Fair Value, Inputs, Level 2 [Member]
Cash and Cash Equivalents [Line Items]
Certificate of deposits / time deposits	[2]	3,532	3,532	2,930
Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Certificate of deposits / time deposits	[2]	2,613	2,613	2,812
Fair Value, Inputs, Level 2 [Member] | Marketable Securities [Member]
Cash and Cash Equivalents [Line Items]
Certificate of deposits / time deposits	[2]	$ 919	$ 919	$ 118

[1] Available-for-sale securities are reported at estimated fair value with unrealized gains and losses reported as component of accumulated other comprehensive loss. Proceeds from the sale of available-for-sale securities were $161 and $626 in the three and nine months ended September 30, 2016, respectively.

[2] Held-to-maturity investments are reported at amortized cost.