Investments - Available-For-Sale Securities (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Investment securities in a continuous loss position for greater than 12 months, estimated fair value	$ 485	$ 769
Investment securities in a continuous loss position for greater than 12 months, estimated fair value, unrealized loss	35	40
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
One year or less (including restricted cash of $25)	4,369
One year through two years	1,476
Two years through three years	1,482
Three years through four years	242
Four years through five years	36
Five years through six years	0
Six years through seven years	0
Seven years through eight years	5
Eight years through nine years	0
Nine years through ten years	0
Estimated Fair Value	7,610
Corporate debt securities | Subsidiary | Non-US
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Unrealized Losses	(55)
Estimated Fair Value	1,100
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	4,433	3,394
Gross Unrealized Gains	950	921
Gross Unrealized Losses	(56)	(16)
Estimated Fair Value	5,327	4,299
Short-term Investments | Corporate debt securities
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	4,349	3,302
Gross Unrealized Gains	2	1
Gross Unrealized Losses	(56)	(16)
Estimated Fair Value	4,295	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	948	920
Gross Unrealized Losses	0	0
Estimated Fair Value	957	929
Long-Term Investment
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	3,266	3,327
Gross Unrealized Gains	16	7
Gross Unrealized Losses	(42)	(67)
Estimated Fair Value	3,240	3,267
Long-Term Investment | Corporate debt securities
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Gross Amortized Cost	3,266	3,327
Gross Unrealized Gains	16	7
Gross Unrealized Losses	(42)	(67)
Estimated Fair Value	$ 3,240	$ 3,267