Investments - Available-For-Sale Securities (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
One year or less (including restricted cash of $25)	$ 4,942
One year through two years	1,418
Two years through three years	1,817
Three years through four years	127
Four years through five years	44
Five years through six years	15
Six years through seven years	3
Seven years through eight years	0
Eight years through nine years	0
Nine years through ten years	0
Estimated Fair Value	8,366
Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Restricted cash	25	$ 28
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	4,961	3,394
Gross Unrealized Gains	1,137	921
Gross Unrealized Losses	(13)	(16)
Estimated Fair Value	6,085	4,299
Short-term Investments | Corporate debt securities
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	4,877	3,302
Gross Unrealized Gains	2	1
Gross Unrealized Losses	(13)	(16)
Estimated Fair Value	4,866	3,287
Short-term Investments | Government and agency securities
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	50	55
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	50	55
Short-term Investments | Equity instruments
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	9	9
Gross Unrealized Gains	1,135	920
Gross Unrealized Losses	0	0
Estimated Fair Value	1,144	929
Long-term Investments
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	3,400	3,327
Gross Unrealized Gains	30	7
Gross Unrealized Losses	(5)	(67)
Estimated Fair Value	3,425	3,267
Long-term Investments | Corporate debt securities
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	3,333	3,327
Gross Unrealized Gains	29	7
Gross Unrealized Losses	(5)	(67)
Estimated Fair Value	3,357	$ 3,267
Long-term Investments | Government and agency securities
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	67
Gross Unrealized Gains	1
Gross Unrealized Losses	0
Estimated Fair Value	$ 68