Senior Notes - Summary of Outstanding Senior Notes (Detail) - USD ($)	1 Months Ended	9 Months Ended
Aug. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
3.45% Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Aggregate Principal Amount		$ 250,000,000
Maturity Date		Nov. 01, 2023
Interest rate Coupon, senior notes		3.45%	3.45%
Interest rate Effective, senior notes		3.50%
Semiannual Interest Payment Dates		May 1 and November 1
7.875% Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Aggregate Principal Amount	$ 500,000,000	$ 500,000,000
Maturity Date	Aug. 15, 2025	Aug. 15, 2025
Interest rate Coupon, senior notes	7.875%	7.875%	7.875%
Interest rate Effective, senior notes		8.00%
Semiannual Interest Payment Dates		February 15 and August 15
5.70% Senior Notes due 2039 [Member]
Debt Instrument [Line Items]
Aggregate Principal Amount		$ 500,000,000
Maturity Date		Oct. 15, 2039
Interest rate Coupon, senior notes		5.70%	5.70%
Interest rate Effective, senior notes		5.75%
Semiannual Interest Payment Dates		April 15 and October 15
4.875% Senior Notes due 2043 [Member]
Debt Instrument [Line Items]
Aggregate Principal Amount		$ 750,000,000
Maturity Date		Nov. 01, 2043
Interest rate Coupon, senior notes		4.875%	4.875%
Interest rate Effective, senior notes		4.89%
Semiannual Interest Payment Dates		May 1 and November 1

Debt instruments semiannual Interest payment date.

No definition available.

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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Balance Type:	na
Period Type:	instant

- 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.

+ Details

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

+ Details

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Period Type:	duration

- Details

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