Financial Instruments (Narrative) (Detail) gal in Millions, $ in Millions	3 Months Ended
Mar. 31, 2019 USD ($) gal	Mar. 31, 2018 USD ($)
Schedule of Cost-method Investments [Line Items] (Deprecated 2018-01-31)
Document Period End Date	Mar. 31, 2019
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ 5
Derivative Instruments, Gain (Loss) Recognized in Income, Net	12	$ (16)
Interest Rate Caps [Member]
Schedule of Cost-method Investments [Line Items] (Deprecated 2018-01-31)
Absolute notional values of derivative instruments	8,335
Interest Rate Caps [Member] \| Subsidiaries [Member]
Schedule of Cost-method Investments [Line Items] (Deprecated 2018-01-31)
Absolute notional values of derivative instruments	3,000
Interest Rate Swaps [Member]
Schedule of Cost-method Investments [Line Items] (Deprecated 2018-01-31)
Absolute notional values of derivative instruments	1,500
Currency Swap [Member]
Schedule of Cost-method Investments [Line Items] (Deprecated 2018-01-31)
Absolute notional values of derivative instruments	$ 1,839
Commodity Contracts [Member]
Schedule of Cost-method Investments [Line Items] (Deprecated 2018-01-31)
Units Of Gasoline \| gal	14
Purchase [Member]
Schedule of Cost-method Investments [Line Items] (Deprecated 2018-01-31)
Absolute notional values of derivative instruments	$ 2,700
Sold [Member]
Schedule of Cost-method Investments [Line Items] (Deprecated 2018-01-31)
Absolute notional values of derivative instruments	5,700
Not Designated As Hedging Instruments [Member] \| Commodity Contracts [Member]
Schedule of Cost-method Investments [Line Items] (Deprecated 2018-01-31)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	3	0
Interest Expense [Member]
Schedule of Cost-method Investments [Line Items] (Deprecated 2018-01-31)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	4	13
Operating Expense [Member]
Schedule of Cost-method Investments [Line Items] (Deprecated 2018-01-31)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 5	$ 4

Units Of Gasoline

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- Definition

The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD.

+ References

No definition available.

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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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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

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

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- Definition

The estimated net amount of unrealized gains or losses on interest rate cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=112277219&loc=d3e80748-113994

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