Income Effect of Derivative Financial Instruments (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 14	$ 280	$ 167	$ 835
Designated as Hedging Instrument [Member] \| Fair Value Hedging [Member] \| Interest Rate Contract [Member]
Derivative [Line Items]
Net interest settlements and accruals excluded from the assessment of hedge effectiveness	50	95	182	292
Ineffectiveness	0	(1)	0	21
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	(40)	(228)	(95)	655
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	40	227	95	(634)
Not Designated as Hedging Instrument [Member] \| Interest Rate Contract [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	20	21	57	(70)
Not Designated as Hedging Instrument [Member] \| Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(61)	37	(151)	129
Not Designated as Hedging Instrument [Member] \| Cross Currency Interest Rate Contract [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 5	$ 128	$ 79	$ 463

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a),(c),(d),(e)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624171-113959

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The net gain (loss) included in earnings for the period relating to components of the gain (loss) on interest rate fair value hedging instruments excluded from the assessment of fair value hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

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- Definition

The net gain (loss) recognized in earnings during the period due to the ineffectiveness on interest rate fair value hedges.

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