Financial Instruments - Cumulative Basis Adjustments for Fair Value Hedges (Details) $ in Millions	Dec. 31, 2018 USD ($)
Short-term debt
Amounts recorded in the Consolidated Statement of Financial Position related to cumulative basis adjustments for fair value hedges
Carrying Amount of the Hedged Item Assets/(Liabilities)	$ (1,878)
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of Assets/(Liabilities)	(4)
Hedging adjustments on discontinued hedging relationships	(6)
Long-term debt
Amounts recorded in the Consolidated Statement of Financial Position related to cumulative basis adjustments for fair value hedges
Carrying Amount of the Hedged Item Assets/(Liabilities)	(6,004)
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of Assets/(Liabilities)	(333)
Hedging adjustments on discontinued hedging relationships	$ (213)

Amount of cumulative increase (decrease) in fair value of hedged liability in fair value hedge, attributable to hedged risk, remaining after discontinued hedge.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109999712-113959

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of liability hedged in fair value hedging relationship.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109999712-113959

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of cumulative increase (decrease) in fair value of hedged liability in fair value hedge, attributable to hedged risk.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109999712-113959

+ Details

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- References

No definition available.

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