Derivative Financial Instruments and Hedging Activities - Derivatives Income (Losses) Recognized in Income (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivatives, Fair Value [Line Items]
Total	$ 108	$ 8	$ 217	$ 30
Cash Flow Hedging [Member]
Derivatives, Fair Value [Line Items]
Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	24	2	46	(2)
Gains (Losses) Reclassified From Accumulated Other Comprehensive Loss Into Income	(27)	(3)	(60)	(3)
Cash Flow Hedging [Member] \| Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	0	2	1	(2)
Gains (Losses) Reclassified From Accumulated Other Comprehensive Loss Into Income	(1)	1	0	1
Cash Flow Hedging [Member] \| Foreign Currency Contracts [Member]
Derivatives, Fair Value [Line Items]
Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	24	0	45	0
Gains (Losses) Reclassified From Accumulated Other Comprehensive Loss Into Income	(26)	(4)	(60)	(4)
Designated as Hedging Instrument [Member] \| Fair Value Hedging [Member] \| Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts	9	6	38	26
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts	2	(1)	1	(2)
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Foreign Currency Contracts [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts	44	(1)	99	(1)
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts	16	4	7	7
Foreign currency derivatives	$ 37	$ 0	$ 72	$ 0

Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge 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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- Definition

The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4D
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624177-113959

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- Definition

The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

+ References

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- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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Amount of gain (loss) recognized in earnings in the period from the increase (decrease) in fair value of foreign currency derivatives not designated as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959

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- Definition

Amount of gain (loss) included in earnings for the period from the increase (decrease) in fair value of interest rate derivatives not designated as hedging instruments.

+ 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=84234895&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 (e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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