Investments - Available-For-Sale Securities (Details) - USD ($) $ in Millions	Sep. 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 $24)	$ 4,790
One year through two years	1,492
Two years through three years	1,949
Three years through four years	115
Four years through five years	223
Five years through six years	30
Six years through seven years	1
Estimated Fair Value	8,600
Restricted cash	24
Short-term Investments
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	4,812	$ 3,394
Gross Unrealized Gains	1,495	921
Gross Unrealized Losses	(15)	(16)
Estimated Fair Value	6,292	4,299
Short-term Investments | Restricted cash
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	24	28
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	24	28
Short-term Investments | Corporate debt securities
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	4,763	3,302
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(15)	(16)
Estimated Fair Value	4,749	3,287
Short-term Investments | Government and agency securities
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	16	55
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	16	55
Short-term Investments | Equity instruments
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	9	9
Gross Unrealized Gains	1,494	920
Gross Unrealized Losses	0	0
Estimated Fair Value	1,503	929
Long-term Investments
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	3,789	3,327
Gross Unrealized Gains	26	7
Gross Unrealized Losses	(4)	(67)
Estimated Fair Value	3,811	3,267
Long-term Investments | Corporate debt securities
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	3,738	3,327
Gross Unrealized Gains	25	7
Gross Unrealized Losses	(4)	(67)
Estimated Fair Value	3,759	$ 3,267
Long-term Investments | Government and agency securities
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	51
Gross Unrealized Gains	1
Gross Unrealized Losses	0
Estimated Fair Value	$ 52