Financial Instruments (Cash, Cash Equivalents and Marketable Securities) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Line Items]
Cash		$ 1,892	$ 1,938
Cash, cash equivalents and marketable securities		4,605	5,300
Marketable securities		1,362	906
Proceeds from sale of available-for-sale securities		788	75
Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Cash		1,892	1,938
Marketable Securities [Member]
Cash and Cash Equivalents [Line Items]
Cash		0	0
Fair Value, Inputs, Level 1 [Member]
Cash and Cash Equivalents [Line Items]
Money market funds		0	550
U.S. Treasury securities	[1]	0	788
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Money market funds		0	550
U.S. Treasury securities	[1]	0	0
Fair Value, Inputs, Level 1 [Member] | Marketable Securities [Member]
Cash and Cash Equivalents [Line Items]
Money market funds		0	0
U.S. Treasury securities	[1]	0	788
Fair Value, Inputs, Level 2 [Member]
Cash and Cash Equivalents [Line Items]
Certificate of deposit / time deposits	[2]	4,075	2,930
Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Certificate of deposit / time deposits	[2]	2,713	2,812
Fair Value, Inputs, Level 2 [Member] | Marketable Securities [Member]
Cash and Cash Equivalents [Line Items]
Certificate of deposit / time deposits	[2]	$ 1,362	$ 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 $788 and $75 in the years ended December 31, 2016, and 2015, respectively.

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