Cash, Cash Equivalents, and Marketable Securities (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total cash and cash equivalents	$ 7,570	$ 8,886	$ 6,767	$ 6,179
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	1,447	266
Marketable securities	4,517	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	6,123	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	974	0
Marketable securities	1,888	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	55	0
Marketable securities	1,556	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	353	266
Marketable securities	739	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	65	0
Marketable securities	290	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	$ 44	$ 40