Cash, Cash Equivalents, and Marketable Securities (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total cash and cash equivalents	$ 5,675	$ 8,886	$ 6,913	$ 6,179
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	334	266
Marketable securities	4,180	2,723
Investment Type [Member] | Fair Value, Estimate Not Practicable, Carrying (Reported) Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash, time deposits and money market funds	5,341	8,620
U.S. government | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	0	0
Marketable securities	1,724	298
U.S. government agencies | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	4	0
Marketable securities	1,354	1,169
Foreign Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	280	266
Marketable securities	520	832
Corporate debt | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	50	0
Marketable securities	540	384
Other Debt Obligations [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable securities	$ 42	$ 40