Financial Instruments Financial Insttruments (Schedule of Cash, Cash Equivalents and Marketable Securities) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Line Items]
Cash			$ 1,515	$ 1,892
Cash and cash equivalents		$ 4,166	3,347	4,605	$ 5,300
Marketable securities			2,570	1,362
Proceeds from Sale of Available-for-sale Securities		$ 260
Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Cash			1,515	1,892
Marketable Securities [Member]
Cash and Cash Equivalents [Line Items]
Cash			0	0
Fair Value, Inputs, Level 2 [Member]
Cash and Cash Equivalents [Line Items]
Certificate of deposits / time deposits	[1]		4,402	4,075
Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Certificate of deposits / time deposits	[1]		1,832	2,713
Fair Value, Inputs, Level 2 [Member] | Marketable Securities [Member]
Cash and Cash Equivalents [Line Items]
Certificate of deposits / time deposits	[1]		$ 2,570	$ 1,362

[1] Represents held-to-maturity investments reported at amortized cost.