Derivative instruments (Hedged Liabilities and Cumulative Amount) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Current portion of long-term debt [Member]
Derivative [Line Items]
Hedged Liability, Discontinued Fair Value Hedge	$ 1,000	$ 500
Carrying amounts of hedged liabilities	2,398	500
Cumulative amounts of fair value hedging adjustments related to the carrying amounts of the hedged liabilities	0	23
Carrying value with discontinued hedging relationships	11	23
Long-term debt [Member]
Derivative [Line Items]
Hedged Liability, Discontinued Fair Value Hedge	137	1,100
Carrying amounts of hedged liabilities	7,905	10,516
Cumulative amounts of fair value hedging adjustments related to the carrying amounts of the hedged liabilities	(217)	(11)
Carrying value with discontinued hedging relationships	$ 37	$ 40

Hedged Liability, Discontinued Fair Value Hedge

No definition available.

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- Definition

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.

+ References

No definition available.

+ Details

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- Definition

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

+ 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 (d)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109999712-113959

+ Details

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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_
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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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