Convertible Debt - Additional Information (Detail) (USD $)	1 Months Ended		12 Months Ended			1 Months Ended			12 Months Ended		1 Months Ended	12 Months Ended		0 Months Ended		1 Months Ended	12 Months Ended		0 Months Ended	1 Months Ended	3 Months Ended		1 Months Ended		3 Months Ended
	Jul. 31, 2012	Nov. 30, 2006	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jul. 31, 2012 Interest rate swap contract	Apr. 30, 2012 Interest rate swap contract	Nov. 30, 2011 Interest rate swap contract	Dec. 31, 2012 Interest rate swap contract	Dec. 31, 2010 Interest rate swap contract	Nov. 30, 2006 Convertible Senior Notes 2013	Dec. 31, 2012 Convertible Senior Notes 2013	Nov. 13, 2006 Convertible Senior Notes 2013	Jan. 09, 2012 Convertible Senior Notes 2011	Nov. 13, 2006 Convertible Senior Notes 2011	Nov. 30, 2006 Convertible Senior Notes 2011 and 2013	Dec. 31, 2012 Convertible Senior Notes 2011 and 2013	Dec. 31, 2011 Convertible Senior Notes 2011 and 2013	Jan. 09, 2012 Purchased Options	Nov. 30, 2006 Purchased Options	Dec. 31, 2011 Purchased Options Group 1	Dec. 31, 2012 Purchased Options Group 2	Nov. 30, 2006 Sold Warrants	Nov. 13, 2006 Sold Warrants	Mar. 31, 2012 Exercised Warrants
Issuance date		Nov. 13, 2006
Senior Notes													$ 1,725,000,000		$ 1,725,000,000
Proceeds from issuance of senior unsecured obligations																3,450,000,000
Cash payment to noteholders for outstanding principal of converted Notes			1,699,816,000	0	0									1,699,800,000
Shares issued to noteholders for the excess of the conversion value over the principal amount of converted Notes														29,500,000
Value of the conversion value over the principal amount of converted Notes														661,400,000
Business day period												5 days
Trading-day period												5 days
Product of last reported sale price and the conversion rate												98.00%
Number of trading days												20 days
Trading day period during quarter												30 days
Ratio of stock price to conversion price												130.00%
Observation period												20 days
Conversion rate for the 2013 Notes will be 62.1978 shares of our common stock per one thousand dollars of principal amount of 2013 Notes												62.1978
Conversion ratio, principal amount basis												1,000
Conversion premium												27.50%
Conversion price												$ 16.08
Amount of converted Notes												14,900,000
Convertible debt, carrying amount												1,652,400,000
Convertible debt, fair value												2,665,700,000
Carrying amount of the equity component												325,100,000
Debt Instrument, unamortized discount												57,700,000
Semi-annual interest rate													1.75%
Debt Instrument, frequency of periodic payment											semi-annually
Effective interest rate																	5.60%	5.60%
Incremental common shares attributable to call options and warrants																				215,000,000			215,000,000
Aggregate amount paid for purchased options			69,905,000	140,993,000	0															669,100,000
Purchased options exercised																					107,500,000
Purchased options shares received																			29,500,000
Purchased options remaining																						107,500,000
Common stock at an exercise price																							$ 19.55	$ 19.55
Proceeds from issuance of warrants																							391,100,000
Shares issues for exercised warrants																									32,300,000
Conversion premium based on the closing price																							55.00%
Closing price per share																								$ 12.61
Aggregate notional amount of interest rate swap contracts designated as cash flow hedges										900,000,000
Realized loss on replaced interest rate swap contracts	45,500,000					45,500,000	23,000,000	141,000,000
Accumulated realized losses in other comprehensive income related to previously-anticipated interest payments reclassified from other comprehensive income and recognized in the consolidated income statements			39,500,000						39,500,000
Unrealized gain on derivatives			$ (108,645,000)	$ (100,446,000)					$ 176,500,000