Fair Values of Certain Financial Liabilities and Other Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Quoted Prices in Active Markets for Indentical Assets (Level 1) | Senior Notes | Carrying (Reported) Amount, Fair Value Disclosure
Financial liabilities
Senior notes (Level 1)	$ 2,647	$ 3,038
Quoted Prices in Active Markets for Indentical Assets (Level 1) | Senior Notes | Portion at Fair Value, Fair Value Disclosure
Financial liabilities
Senior notes (Level 1)	2,766	3,296
Quoted Prices in Active Markets for Indentical Assets (Level 1) | Convertible Debt | Carrying (Reported) Amount, Fair Value Disclosure
Financial liabilities
Exchangeable Senior Debentures (Level 1)	371	531
Quoted Prices in Active Markets for Indentical Assets (Level 1) | Convertible Debt | Portion at Fair Value, Fair Value Disclosure
Financial liabilities
Exchangeable Senior Debentures (Level 1)	603	725
Significant Other Observable Inputs (Level 2) | Credit Facility | Carrying (Reported) Amount, Fair Value Disclosure
Financial liabilities
Credit facility (Level 2)	946	763
Significant Other Observable Inputs (Level 2) | Credit Facility | Portion at Fair Value, Fair Value Disclosure
Financial liabilities
Credit facility (Level 2)	946	763
Significant Other Observable Inputs (Level 2) | Mortgage Backed Securities, Other | Carrying (Reported) Amount, Fair Value Disclosure
Financial liabilities
Mortgage debt and other, excluding capital leases (Level 2)	793	1,078
Significant Other Observable Inputs (Level 2) | Mortgage Backed Securities, Other | Portion at Fair Value, Fair Value Disclosure
Financial liabilities
Mortgage debt and other, excluding capital leases (Level 2)	$ 802	$ 1,094