Components of Debt (Parenthetical) (Detail)			9 Months Ended
	Sep. 30, 2013 Debentures Eleven Point Two Five Percent Due February One Two Thousand Nineteen Scenario, Adjustment	Dec. 31, 2012 Debentures Eleven Point Two Five Percent Due February One Two Thousand Nineteen Scenario, Adjustment	Sep. 30, 2013 Debentures Eleven Point Two Five Percent Due February One Two Thousand Nineteen Scenario, Actual		Sep. 30, 2013 Senior Notes Four Point Nine Five Percent Due April One Two Thousand Fourteen	Sep. 30, 2013 Senior Notes Five Point Five Zero Percent Due May Fifteen Two Thousand Fifteen	Sep. 30, 2013 Senior Notes Eight Point Six Zero Percent Due August Fifteen Two Thousand Sixteen	Sep. 30, 2013 Senior Notes Six Point One Two Five Percent Due January Fifteen Two Thousand Seventeen	Sep. 30, 2013 Senior Notes Seven Point Two Five Percent Due May Fifteen Two Thousand Eighteen	Sep. 30, 2013 Senior Notes Eight Point Two Five Percent Due March Fifteen Two Thousand Nineteen	Sep. 30, 2013 Senior Notes Seven Point Six Two Five Percent Due June Fifteen Two Thousand Twenty	Sep. 30, 2013 Senior Notes Seven Point Eight Seven Five Percent Due March Fifteen Two Thousand Twenty One	Sep. 30, 2013 Debentures Eight Point Eight Seven Five Percent Due April Fifteen Two Thousand Twenty One	Sep. 30, 2013 Senior Notes Seven Point Zero Percent Due February Fifteen Two Thousand Twenty Two	Sep. 30, 2013 Debentures Six Point Six Two Five Percent Due April Fifteen Two Thousand Twenty Nine	Sep. 30, 2013 Debentures Eight Point Eight Two Zero Percent Due April Fifteen Two Thousand Thirty One
Debt Instrument [Line Items]
Interest rate	12.50%	12.50%	11.25%	[1]	4.95%	5.50%	8.60%	6.125%	7.25%	8.25%	7.625%	7.875%	8.875%	7.00%	6.625%	8.82%
Maturity date			Feb. 01, 2019		Apr. 01, 2014	May 15, 2015	Aug. 15, 2016	Jan. 15, 2017	May 15, 2018	Mar. 15, 2019	Jun. 15, 2020	Mar. 15, 2021	Apr. 15, 2021	Feb. 15, 2022	Apr. 15, 2029	Apr. 15, 2031

[1] As of September 30, 2013 and December 31, 2012, the interest rate on the 11.25% senior notes due February 1, 2019 was 12.50% as a result of downgrades in the ratings of the notes by the rating agencies.