Fair Value Measurements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Security, Maturity Period for Classification as Cash Equivalent	three months or less
Investment Security, Maturity Period for Classification as Marketable Security	greater than three months
Fair Value Measurement, Period After Which Fair Value of Collateral is Adjusted	greater than 120 days past due
Fair Value of Derivative Assets	$ 924	$ 859
Fair Value of Derivative Liabilities	243	167
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents - financial instruments	266	351
Marketable securities	2,723	3,258
Fair Value of Derivative Assets	924	859
Total assets at fair value	3,913	4,468
Fair Value of Derivative Liabilities	243	167
Total liabilities at fair value	243	167
Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Par value assets excluded from fair value by input	6,300	3,800
Fair Value, Measurements, Recurring [Member] | Cash [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Par value assets excluded from fair value by input	2,300	2,000
Fair Value, Measurements, Recurring [Member] | Foreign Government and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents - financial instruments	266	341
Marketable securities	832	405
Fair Value, Measurements, Recurring [Member] | Corporate debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents - financial instruments	0	10
Marketable securities	384	1,555
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable securities	1,467	1,268
Fair Value, Measurements, Recurring [Member] | Other Marketable Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable securities	40	30
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents - financial instruments	0	0
Marketable securities	298	17
Fair Value of Derivative Assets	0	0
Total assets at fair value	298	17
Fair Value of Derivative Liabilities	0	0
Total liabilities at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Foreign Government and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents - financial instruments	0	0
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Corporate debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents - financial instruments	0	0
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable securities	298	17
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Other Marketable Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents - financial instruments	266	351
Marketable securities	2,425	3,241
Fair Value of Derivative Assets	924	859
Total assets at fair value	3,615	4,451
Fair Value of Derivative Liabilities	243	167
Total liabilities at fair value	243	167
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Foreign Government and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents - financial instruments	266	341
Marketable securities	832	405
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents - financial instruments	0	10
Marketable securities	384	1,555
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable securities	1,169	1,251
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Other Marketable Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable securities	$ 40	$ 30