Derivative Financial Instruments and Hedging Activities (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Derivative [Line Items]
Debt Carrying Value Fair Value	$ 41,600		$ 39,400
Income Effect of Derivative Financial Instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	27	$ (201)
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Fair Value of Derivative Assets	2,420		1,128
Fair Value of Derivative Liabilities	801		356
Derivative, Notional Amount	105,425		106,880
Derivative, Collateral, Obligation to Return Cash	23		18
Derivative, Collateral, Right to Reclaim Cash	86		78
Derivative Asset, Not Offset, Policy Election Deduction	451		169
Interest Rate Contract [Member] \| Designated as Hedging Instrument [Member] \| Fair Value Hedging [Member]
Income Effect of Derivative Financial Instruments [Abstract]
Net interest settlements and accruals excluded from the assessment of hedge effectiveness	28	(20)
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	1,110	250
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	(1,093)	(253)
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Derivative, Notional Amount	23,663		26,577
Interest Rate Contract [Member] \| Designated as Hedging Instrument [Member] \| Level 2 [Member] \| Fair Value, Recurring [Member] \| Fair Value Hedging [Member]
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Fair Value of Derivative Assets	1,549		702
Fair Value of Derivative Liabilities	0		19
Interest Rate Contract [Member] \| Not Designated as Hedging Instrument [Member]
Income Effect of Derivative Financial Instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	(74)	(27)
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Derivative, Notional Amount	72,822		68,914
Interest Rate Contract [Member] \| Not Designated as Hedging Instrument [Member] \| Level 2 [Member] \| Fair Value, Recurring [Member]
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Fair Value of Derivative Assets	651		275
Fair Value of Derivative Liabilities	561		191
Foreign Exchange Contract [Member] \| Not Designated as Hedging Instrument [Member]
Income Effect of Derivative Financial Instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	207	(6)
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Derivative, Notional Amount	3,002		5,540
Foreign Exchange Contract [Member] \| Not Designated as Hedging Instrument [Member] \| Level 2 [Member] \| Fair Value, Recurring [Member]
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Fair Value of Derivative Assets	94		17
Fair Value of Derivative Liabilities	2		79
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	(151)	$ (145)
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Derivative, Notional Amount	5,938		5,849
Cross Currency Interest Rate Contract [Member] \| Not Designated as Hedging Instrument [Member] \| Level 2 [Member] \| Fair Value, Recurring [Member]
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Fair Value of Derivative Assets	126		134
Fair Value of Derivative Liabilities	$ 238		$ 67

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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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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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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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