Carrying Value of Long-Term Debt of Outstanding (Detail) - Senior Notes - USD ($)	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Long-term debt	$ 3,825,000,000	$ 2,600,000,000
$500 million, 6.45% due June 1, 2016
Debt Instrument [Line Items]
Long-term debt	0	517,000,000
Senior notes	$ 500,000,000	$ 500,000,000
Debt instrument, stated interest rate	6.45%	6.45%
$500 million, 7.20% due June 15, 2018
Debt Instrument [Line Items]
Long-term debt	$ 504,000,000	$ 505,000,000
Senior notes	$ 500,000,000	$ 500,000,000
Debt instrument, stated interest rate	7.20%	7.20%
$300 million, 6.30% due August 1, 2018
Debt Instrument [Line Items]
Long-term debt	$ 312,000,000	$ 314,000,000
Senior notes	$ 300,000,000	$ 300,000,000
Debt instrument, stated interest rate	6.30%	6.30%
$400 million, 2.625% due October 1, 2019
Debt Instrument [Line Items]
Long-term debt	$ 400,000,000	$ 0
Senior notes	$ 400,000,000	$ 0
Debt instrument, stated interest rate	2.65%	0.00%
$600 million, 3.15% due December 1, 2022
Debt Instrument [Line Items]
Long-term debt	$ 598,000,000	$ 598,000,000
Senior notes	$ 600,000,000	$ 600,000,000
Debt instrument, stated interest rate	3.15%	3.15%
$600 million, 3.85% due October 1, 2024
Debt Instrument [Line Items]
Long-term debt	$ 599,000,000	$ 0
Senior notes	$ 600,000,000	$ 0
Debt instrument, stated interest rate	3.85%	0.00%
$250 million, 8.15% due June 15, 2038
Debt Instrument [Line Items]
Long-term debt	$ 266,000,000	$ 266,000,000
Senior notes	$ 250,000,000	$ 250,000,000
Debt instrument, stated interest rate	8.15%	8.15%
$400 million, 4.625% due December 1, 2042
Debt Instrument [Line Items]
Long-term debt	$ 400,000,000	$ 400,000,000
Senior notes	$ 400,000,000	$ 400,000,000
Debt instrument, stated interest rate	4.625%	4.625%
$750 million, 4.95% due October 1, 2044
Debt Instrument [Line Items]
Long-term debt	$ 746,000,000	$ 0
Senior notes	$ 750,000,000	$ 0
Debt instrument, stated interest rate	4.95%	0.00%

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

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)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20

-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 9

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+ 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=34725769&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

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