Fair Value of Certain Financial Assets and Liabilities and Other Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Carrying (Reported) Amount, Fair Value Disclosure | Significant Other Observable Inputs (Level 2) | Mortgage Notes
Financial assets
Financial assets		$ 65
Carrying (Reported) Amount, Fair Value Disclosure | Significant Other Observable Inputs (Level 2) | Credit Facility
Financial liabilities
Financial liabilities	763	117
Carrying (Reported) Amount, Fair Value Disclosure | Significant Other Observable Inputs (Level 2) | Mortgage debt and other, net of capital leases
Financial liabilities
Financial liabilities	1,078	1,091
Carrying (Reported) Amount, Fair Value Disclosure | Quoted Prices in Active Markets for Identical Assets (Level 1) | Senior Notes
Financial liabilities
Financial liabilities	3,038	3,641
Carrying (Reported) Amount, Fair Value Disclosure | Quoted Prices in Active Markets for Identical Assets (Level 1) | Exchangeable Senior Debentures
Financial liabilities
Financial liabilities	531	902
Portion at Fair Value, Fair Value Disclosure | Significant Other Observable Inputs (Level 2) | Mortgage Notes
Financial assets
Financial assets		76
Portion at Fair Value, Fair Value Disclosure | Significant Other Observable Inputs (Level 2) | Credit Facility
Financial liabilities
Financial liabilities	763	117
Portion at Fair Value, Fair Value Disclosure | Significant Other Observable Inputs (Level 2) | Mortgage debt and other, net of capital leases
Financial liabilities
Financial liabilities	1,094	1,114
Portion at Fair Value, Fair Value Disclosure | Quoted Prices in Active Markets for Identical Assets (Level 1) | Senior Notes
Financial liabilities
Financial liabilities	3,296	3,772
Portion at Fair Value, Fair Value Disclosure | Quoted Prices in Active Markets for Identical Assets (Level 1) | Exchangeable Senior Debentures
Financial liabilities
Financial liabilities	$ 725	$ 1,076