Fair Value Measurements - Unobservable Data Used in Recurring Valuations of Level 3 (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Interest Rate Swaps [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative financial instruments, Fair Value	$ 203	$ 357
Cross-Currency Interest Rate Swaps [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative financial instruments, Fair Value	(366)	(1,296)
Other [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative financial instruments, Fair Value	(18)	$ (13)
Level 3 [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative financial instruments, Fair Value	(381)
Level 3 [Member] \| Cross-Currency Interest Rate Swaps [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative financial instruments, Fair Value	$ (322)
Discounted cash flow	Discounted Cash Flow, Constant Prepayment Rate
Constant prepayment rate	4.00%
Level 3 [Member] \| Other [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative financial instruments, Fair Value	$ (18)
Level 3 [Member] \| Prime/LIBOR Basis Swaps [Member] \| Interest Rate Swaps [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative financial instruments, Fair Value	$ (41)
Discounted cash flow	Discounted Cash Flow, Constant Prepayment Rate
Constant prepayment rate	6.00%
Level 3 [Member] \| Prime/LIBOR Basis Swaps [Member] \| Interest Rate Swaps [Member] \| Minimum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Bid/ask adjustment to discount rate	0.08%
Level 3 [Member] \| Prime/LIBOR Basis Swaps [Member] \| Interest Rate Swaps [Member] \| Maximum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Bid/ask adjustment to discount rate	0.08%
Level 3 [Member] \| Prime/LIBOR Basis Swaps [Member] \| Interest Rate Swaps [Member] \| Weighted Average [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Bid/ask adjustment to discount rate	0.08%

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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Adjustment to the discount rate used to measure fair value for lack of ability to convert business interests into cash quickly.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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