Carrying Value of Long-Term Debt of Outstanding (Detail) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Short-term borrowings	$ 299,000,000	$ 0
Senior Notes
Debt Instrument [Line Items]
Long-term debt	3,821,000,000	3,825,000,000
$500 million, 6.45% due June 1, 2016 \| Senior Notes
Debt Instrument [Line Items]
Senior notes		$ 500,000,000
Debt instrument, stated interest rate		6.45%
$500 million, 7.20% due June 15, 2018 \| Senior Notes
Debt Instrument [Line Items]
Long-term debt	503,000,000	$ 504,000,000
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 \| Senior Notes
Debt Instrument [Line Items]
Long-term debt	$ 309,000,000	$ 312,000,000
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 \| Senior Notes
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	2.65%	2.65%
$600 million, 3.15% due December 1, 2022 \| Senior Notes
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 \| Senior Notes
Debt Instrument [Line Items]
Long-term debt	$ 599,000,000	$ 599,000,000
Senior notes	$ 600,000,000	$ 600,000,000
Debt instrument, stated interest rate	3.85%	3.85%
$250 million, 8.15% due June 15, 2038 \| Senior Notes
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 \| Senior Notes
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 \| Senior Notes
Debt Instrument [Line Items]
Long-term debt	$ 746,000,000	$ 746,000,000
Senior notes	$ 750,000,000	$ 750,000,000
Debt instrument, stated interest rate	4.95%	4.95%
Commercial Paper
Debt Instrument [Line Items]
Short-term borrowings	$ 299,000,000	$ 0

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.

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