Derivative Financial Instruments and Hedging Activities (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Effect of Derivative Financial Instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	$ 594	$ (194)	$ (157)
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Fair Value of Derivative Assets	2,601	1,128
Fair Value of Derivative Liabilities	524	356
Derivative, Collateral, Obligation to Return Cash	9	18
Derivative, Collateral, Right to Reclaim Cash	96	78
Derivative Asset, Not Offset, Policy Election Deduction	204	169
Derivative, Notional Amount	109,354	106,880
Interest Rate Contract [Member] \| Not Designated as Hedging Instrument [Member]
Income Effect of Derivative Financial Instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	(100)	(13)	(84)
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Derivative, Notional Amount	70,318	68,914
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	290	(16)	10
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	986	706	(155)
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	(985)	(694)	153
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Derivative, Notional Amount	26,924	26,577
Interest Rate Contract [Member] \| Currency Swap [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	(2)	0	0
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	38	0	0
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	(37)	0	0
Foreign Exchange Contract [Member] \| Not Designated as Hedging Instrument [Member]
Income Effect of Derivative Financial Instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	(82)	52	163
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Derivative, Notional Amount	4,378	5,540
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	486	(229)	$ (244)
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Derivative, Notional Amount	6,849	5,849
Cross Currency Interest Rate Contract [Member] \| Fair Value Hedging [Member] \| Designated as Hedging Instrument [Member]
Balance Sheet Effect of Derivative Financial Instruments [Abstract]
Derivative, Notional Amount	885	0
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	663	275
Fair Value of Derivative Liabilities	439	191
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	1,331	702
Fair Value of Derivative Liabilities	4	19
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	4	17
Fair Value of Derivative Liabilities	80	79
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	557	134
Fair Value of Derivative Liabilities	1	67
Level 2 [Member] \| Fair Value, Measurements, Recurring [Member] \| Cross Currency 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	46	0
Fair Value of Derivative Liabilities	$ 0	$ 0

Balance Sheet Effect of Derivative Financial Instruments [Abstract]

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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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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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