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Derivative Financial Instruments and Hedging Activities - Derivatives Income (Losses) Recognized in Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Total		$ 292	$ 56
Interest expense	$ 3,225	2,566	1,972
Operating expenses	1,522	1,390	1,250
Derivatives Designated as Hedges [Member] \| Fair Value Hedging [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts		42	(7)
Derivatives Designated as Hedges [Member] \| Cash Flow Hedging [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts		3	(3)
Derivatives Designated as Hedges [Member] \| Cash Flow Hedging [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts		121	39
Derivatives not Designated as Hedges [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts		40	27
Foreign currency derivatives		86	0
Operating Expenses [Member]
Derivatives, Fair Value [Line Items]
Total	(255)
Operating Expenses [Member] \| Derivatives Designated as Hedges [Member] \| Fair Value Hedging [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Hedged items	0
Interest rate contracts and Foreign currency contracts	0
Operating Expenses [Member] \| Derivatives Designated as Hedges [Member] \| Fair Value Hedging [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Hedged items	(17)
Interest rate contracts and Foreign currency contracts	18
Operating Expenses [Member] \| Derivatives Designated as Hedges [Member] \| Cash Flow Hedging [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts	0
Operating Expenses [Member] \| Derivatives Designated as Hedges [Member] \| Cash Flow Hedging [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts	(114)
Operating Expenses [Member] \| Derivatives not Designated as Hedges [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts	0
Foreign currency derivatives	(142)
Interest Expense [Member]
Derivatives, Fair Value [Line Items]
Total	(77)
Interest Expense [Member] \| Derivatives Designated as Hedges [Member] \| Fair Value Hedging [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Hedged items	83
Interest rate contracts and Foreign currency contracts	(102)
Interest Expense [Member] \| Derivatives Designated as Hedges [Member] \| Fair Value Hedging [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Hedged items	0
Interest rate contracts and Foreign currency contracts	(5)
Interest Expense [Member] \| Derivatives Designated as Hedges [Member] \| Cash Flow Hedging [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts	14
Interest Expense [Member] \| Derivatives Designated as Hedges [Member] \| Cash Flow Hedging [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts	(49)
Interest Expense [Member] \| Derivatives not Designated as Hedges [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts	26
Foreign currency derivatives	(44)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] \| Cash Flow Hedging [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
(Gains) Losses Reclassified From Accumulated Other Comprehensive Loss Into Income	(7)	(1)	2
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] \| Cash Flow Hedging [Member] \| Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	3	5	4
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Derivatives, Fair Value [Line Items]
(Gains) Losses Reclassified From Accumulated Other Comprehensive Loss Into Income	0	197	0
Accumulated Foreign Currency Adjustment Attributable to Parent [Member] \| Fair Value Hedging [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	(3)	0	0
(Gains) Losses Reclassified From Accumulated Other Comprehensive Loss Into Income	3	0	0
Accumulated Foreign Currency Adjustment Attributable to Parent [Member] \| Cash Flow Hedging [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	(89)	81	(20)
(Gains) Losses Reclassified From Accumulated Other Comprehensive Loss Into Income	86	(86)	31
Accumulated Foreign Currency Adjustment Attributable to Parent [Member] \| Derivatives Designated as Hedges [Member]
Derivatives, Fair Value [Line Items]
Gains reclassified from AOCI into income	11
AOCI Attributable to Parent [Member]
Derivatives, Fair Value [Line Items]
Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	(89)	86	(16)
(Gains) Losses Reclassified From Accumulated Other Comprehensive Loss Into Income	$ 82	$ (87)	$ 33