Schedule of Extinguishment of Debt (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Extinguishment Of Debt [Line Items]
Make-whole premium			$ 63	$ 21
Prepaid interest	$ (1)	$ (3)	(5)	(7)
Loss on extinguishment of debt	(65)	$ (28)	(66)	$ (28)
Tender Offer [Member]
Extinguishment Of Debt [Line Items]
Tender premium	36		36
Make-whole premium	0		0
Prepaid interest	0		0
Unamortized original issue premium	(11)		(11)
Unamortized deferred loan costs	12		12
Loss on extinguishment of debt	37		37
Extinguishment [Member]
Extinguishment Of Debt [Line Items]
Tender premium	0		0
Make-whole premium	25		25
Prepaid interest	2		2
Unamortized original issue premium	(8)		(8)
Unamortized deferred loan costs	9		9
Loss on extinguishment of debt	28		28
Total [Member]
Extinguishment Of Debt [Line Items]
Tender premium	36		36
Make-whole premium	25		25
Prepaid interest	2		2
Unamortized original issue premium	(19)		(19)
Unamortized deferred loan costs	21		21
Loss on extinguishment of debt	$ 65		$ 65

Premium paid for tender offer of unsecured senior notes.

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- Definition

Write-off of amounts previously capitalized as debt issuance premium in an extinguishment of debt.

+ References

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.

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- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=49170532&loc=d3e12317-112629

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
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Amount of interest expense classified as other.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4D
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624177-113959

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-Publisher FASB
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- Definition

Amount of cash outflow for cost from early extinguishment and prepayment of debt. Includes, but is not limited to, third-party cost, premium paid, and other fee paid to lender directly for debt extinguishment or debt prepayment. Excludes accrued interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
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Write-off of amounts previously capitalized as debt issuance cost in an extinguishment of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
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-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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