Derivative Financial Instruments and Hedging Activities - Derivatives Income (Losses) Recognized in Income (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Derivatives, Fair Value [Line Items]
Interest expense	$ 947	$ 732
Operating expenses	370	365
AOCI Attributable to Parent [Member]
Derivatives, Fair Value [Line Items]
Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	(63)	22
(Gains) Losses Reclassified From Accumulated Other Comprehensive Income	48	(21)
Fair Value Hedging [Member] \| Foreign Currency Translation Adjustment [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	(11)	0
(Gains) Losses Reclassified From Accumulated Other Comprehensive Income	11	0
Cash Flow Hedging [Member] \| Foreign Currency Translation Adjustment [Member] \| Foreign Currency Contracts [Member]
Derivatives, Fair Value [Line Items]
Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	(52)	18
(Gains) Losses Reclassified From Accumulated Other Comprehensive Income	39	(18)
Cash Flow Hedging [Member] \| Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] \| Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	0	4
(Gains) Losses Reclassified From Accumulated Other Comprehensive Income	(2)	(3)
Interest Expense [Member]
Derivatives, Fair Value [Line Items]
Total	(65)	(8)
Operating Expense [Member]
Derivatives, Fair Value [Line Items]
Total	(32)	46
Designated as Hedging Instrument [Member] \| Foreign Currency Translation Adjustment [Member]
Derivatives, Fair Value [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	5
Designated as Hedging Instrument [Member] \| Interest Expense [Member] \| Fair Value Hedging [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Hedged items	(210)	208
Interest rate swaps and Foreign currency swaps	181	(210)
Designated as Hedging Instrument [Member] \| Interest Expense [Member] \| Fair Value Hedging [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Hedged items	0	0
Interest rate swaps and Foreign currency swaps	(16)	0
Designated as Hedging Instrument [Member] \| Interest Expense [Member] \| Cash Flow Hedging [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Interest rate swaps and Foreign currency swaps	3	4
Designated as Hedging Instrument [Member] \| Interest Expense [Member] \| Cash Flow Hedging [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Interest rate swaps and Foreign currency swaps	(18)	(9)
Designated as Hedging Instrument [Member] \| Operating Expense [Member] \| Fair Value Hedging [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Hedged items	0	0
Interest rate swaps and Foreign currency swaps	0	0
Designated as Hedging Instrument [Member] \| Operating Expense [Member] \| Fair Value Hedging [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Hedged items	32	0
Interest rate swaps and Foreign currency swaps	(31)	0
Designated as Hedging Instrument [Member] \| Operating Expense [Member] \| Cash Flow Hedging [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Interest rate swaps and Foreign currency swaps	0	0
Designated as Hedging Instrument [Member] \| Operating Expense [Member] \| Cash Flow Hedging [Member] \| Foreign Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Interest rate swaps and Foreign currency swaps	(33)	24
Not Designated as Hedging Instrument [Member] \| Interest Expense [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts	(5)	6
Foreign currency swaps	0	(7)
Not Designated as Hedging Instrument [Member] \| Operating Expense [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts	0	0
Foreign currency swaps	$ 0	$ 22

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

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Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

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Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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Amount of gain (loss) included in earnings for the period from the increase (decrease) in fair value of interest rate derivatives not designated as hedging instruments.

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Amount of the cost of borrowed funds accounted for as interest expense.

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