Financial Instruments (Narrative) (Detail) gal in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) gal	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) gal	Sep. 30, 2015 USD ($)
Schedule of Cost-method Investments [Line Items]
Document Period End Date			Sep. 30, 2016
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ 6		$ 6
Derivative Instruments, Gain (Loss) Recognized in Income, Net	6	$ 14	1	$ 57
Interest Rate Caps [Member]
Schedule of Cost-method Investments [Line Items]
Absolute notional values of derivative instruments	10,152		10,152
Interest Rate Caps [Member] | Subsidiary Issuers [Member]
Schedule of Cost-method Investments [Line Items]
Absolute notional values of derivative instruments	5,000		5,000
Interest Rate Swaps [Member]
Schedule of Cost-method Investments [Line Items]
Absolute notional values of derivative instruments	$ 2,000		$ 2,000
Commodity Contracts [Member]
Schedule of Cost-method Investments [Line Items]
Units Of Gasoline | gal	6		6
Currency Swap [Member]
Schedule of Cost-method Investments [Line Items]
Absolute notional values of derivative instruments	$ 885		$ 885
ERROR in label resolution.
Schedule of Cost-method Investments [Line Items]
Absolute notional values of derivative instruments	2,600		2,600
ERROR in label resolution.
Schedule of Cost-method Investments [Line Items]
Absolute notional values of derivative instruments	7,600		7,600
Not Designated As Hedging Instruments [Member] | Commodity Contracts [Member]
Schedule of Cost-method Investments [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	0	(4)	0	0
Interest Expense [Member]
Schedule of Cost-method Investments [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	8	19	43	21
Operating Expense [Member]
Schedule of Cost-method Investments [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 3	$ 2	$ 26	$ 16