Financial Instruments (Schedule of Cash, Cash Equivalents and Marketable Securities) (Details) - USD ($) $ in Millions		3 Months Ended	6 Months Ended
		Jun. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Cash and Cash Equivalents [Line Items]
Cash		$ 1,658	$ 1,658	$ 1,938
Cash and cash equivalents		4,411	4,411	5,300	$ 4,746	$ 6,910
Marketable securities		742	742	906
Proceeds from sale of available-for-sale securities		205	465
Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Cash		1,658	1,658	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		374	374	550
U.S. Treasury securities	[1]	323	323	788
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Money market funds		374	374	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]	323	323	788
Fair Value, Inputs, Level 2 [Member]
Cash and Cash Equivalents [Line Items]
Certificate of deposits / time deposits	[2]	2,798	2,798	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]	2,379	2,379	2,812
Fair Value, Inputs, Level 2 [Member] | Marketable Securities [Member]
Cash and Cash Equivalents [Line Items]
Certificate of deposits / time deposits	[2]	$ 419	$ 419	$ 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 $205 and $465 in the three and six months ended June 30, 2016, respectively.

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