Derivative Financial Instruments and Hedging Activities (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Derivative [Line Items]
Debt Carrying Value Fair Value	$ 38,100		$ 38,000
Income Effect of Derivative Financial Instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	(201)	$ (71)
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Notional	101,844		109,446
Fair Value of Derivative Assets	631		670
Fair Value of Derivative Liabilities	684		663
Derivative, Collateral, Obligation to Return Cash	26		19
Derivative, Collateral, Right to Reclaim Cash	63		59
Derivative Asset, Not Offset, Policy Election Deduction	219		233
Interest Rate Contract [Member] \| Not Designated as Hedging Instrument [Member]
Income Effect of Derivative Financial Instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	(27)	(17)
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Notional	67,726		76,904
Interest Rate Contract [Member] \| Fair Value Hedging [Member] \| Designated as Hedging Instrument [Member]
Income Effect of Derivative Financial Instruments [Abstract]
Net interest settlements and accruals excluded from the assessment of hedge effectiveness	(20)	26
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	250	(339)
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	(253)	329
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Notional	23,894		22,989
Foreign Exchange Contract [Member] \| Not Designated as Hedging Instrument [Member]
Income Effect of Derivative Financial Instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	(6)	(12)
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Notional	3,893		4,318
Cross Currency Interest Rate Contract [Member] \| Not Designated as Hedging Instrument [Member]
Income Effect of Derivative Financial Instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	(145)	$ (58)
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Notional	6,331		5,235
Level 2 [Member] \| Fair Value, Measurements, Recurring [Member] \| Interest Rate Contract [Member] \| Not Designated as Hedging Instrument [Member]
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Fair Value of Derivative Assets	216		235
Fair Value of Derivative Liabilities	295		274
Level 2 [Member] \| Fair Value, Measurements, Recurring [Member] \| Interest Rate Contract [Member] \| Fair Value Hedging [Member] \| Designated as Hedging Instrument [Member]
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Fair Value of Derivative Assets	217		158
Fair Value of Derivative Liabilities	143		208
Level 2 [Member] \| Fair Value, Measurements, Recurring [Member] \| Foreign Exchange Contract [Member] \| Not Designated as Hedging Instrument [Member]
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Fair Value of Derivative Assets	52		45
Fair Value of Derivative Liabilities	30		24
Level 2 [Member] \| Fair Value, Measurements, Recurring [Member] \| Cross Currency Interest Rate Contract [Member] \| Not Designated as Hedging Instrument [Member]
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Fair Value of Derivative Assets	146		232
Fair Value of Derivative Liabilities	$ 216		$ 157

Balance Sheet Effect of Derivative Financial Instruments [Abstract]

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Fair value of hedged debt carried at cost which approximates fair value

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Income Effect of Derivative Financial Instruments [Abstract]

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Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
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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 the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

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Fair value of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected not to be offset, deducted from derivative assets.

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Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.

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Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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