Components of Debt (Parenthetical) (Detail)					3 Months Ended
	Sep. 20, 2012 Revised Interest Rate Stated Percentage	Aug. 02, 2012 Revised Interest Rate Stated Percentage	Jun. 14, 2012 Revised Interest Rate Stated Percentage	May 17, 2011 Revised Interest Rate Stated Percentage	Mar. 31, 2013 Senior Notes Eleven Point Two Five Percent Due February One Two Thousand Nineteen		Mar. 31, 2013 Senior Notes Four Point Nine Five Percent Due April One Two Thousand Fourteen	Mar. 31, 2013 Senior Notes Eight Point Two Five Percent Due March Fifteen Two Thousand Nineteen	Mar. 31, 2013 Senior Notes Five Point Five Zero Percent Due May Fifteen Two Thousand Fifteen	Mar. 31, 2013 Senior Notes Eight Point Six Zero Percent Due August Fifteen Two Thousand Sixteen	Mar. 31, 2013 Senior Notes Six Point One Two Five Percent Due January Fifteen Two Thousand Seventeen	Mar. 31, 2013 Senior Notes Seven Point Two Five Percent Due May Fifteen Two Thousand Eighteen	Mar. 31, 2013 Senior Notes Seven Point Six Two Five Percent Due June Fifteen Two Thousand Twenty	Mar. 31, 2013 Senior Notes Seven Point Eight Seven Five Percent Due March Fifteen Two Thousand Twenty One	Mar. 31, 2013 Debentures Eight Point Eight Seven Five Percent Due April Fifteen Two Thousand Twenty One	Mar. 31, 2013 Debentures Six Point Six Two Five Percent Due April Fifteen Two Thousand Twenty Nine	Mar. 31, 2013 Debentures Eight Point Eight Two Zero Percent Due April Fifteen Two Thousand Thirty One
Debt Instrument [Line Items]
Interest rate	12.50%	12.25%	12.00%	11.75%	11.25%	[1]	4.95%	8.25%	5.50%	8.60%	6.125%	7.25%	7.625%	7.875%	8.875%	6.625%	8.82%
Maturity date					Feb. 01, 2019	[1]	Apr. 01, 2014	Mar. 15, 2019	May 15, 2015	Aug. 15, 2016	Jan. 15, 2017	May 15, 2018	Jun. 15, 2020	Mar. 15, 2021	Apr. 15, 2021	Apr. 15, 2029	Apr. 15, 2031

[1] On May 17, 2011, June 14, 2012, August 2, 2012 and September 20, 2012, the interest rate on the 11.25% senior notes due February 1, 2019 was increased to 11.75%, 12.0%, 12.25% and 12.50%, respectively, as a result of downgrades in the ratings of the notes by the rating agencies.