Borrowing Arrangements (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Unsecured revolving credit facilities	Dec. 31, 2011 Unsecured revolving credit facilities	Dec. 31, 2012 9% Senior Notes due 2012	Dec. 31, 2011 9% Senior Notes due 2012	Dec. 31, 2012 8 1/4% Senior Notes due 2012	Dec. 31, 2011 8 1/4% Senior Notes due 2012	Dec. 31, 2012 Unsecured term loan due 2013	Dec. 31, 2011 Unsecured term loan due 2013	Dec. 31, 2012 6.25% Senior Notes due 2013	Dec. 31, 2011 6.25% Senior Notes due 2013	Dec. 31, 2012 Unsecured term loan due 2015		Dec. 31, 2011 Unsecured term loan due 2015		Dec. 31, 2012 3.125% Senior Notes due 2015	Dec. 31, 2011 3.125% Senior Notes due 2015	Nov. 30, 2010 3.125% Senior Notes due 2015	Dec. 31, 2012 6% Senior Notes due 2015	Dec. 31, 2011 6% Senior Notes due 2015	Dec. 31, 2012 6 1/2% Senior Notes due 2016	Dec. 31, 2011 6 1/2% Senior Notes due 2016	Dec. 31, 2012 Unsecured term loan due 2017		Dec. 31, 2011 Unsecured term loan due 2017		Dec. 31, 2012 6 3/4% Senior Notes due 2017	Dec. 31, 2011 6 3/4% Senior Notes due 2017	Dec. 31, 2010 6 3/4% Senior Notes due 2017	Dec. 31, 2012 Unsecured term loan due 2018	Dec. 31, 2011 Unsecured term loan due 2018	Dec. 31, 2012 2.00% Senior Notes due 2018	Dec. 31, 2011 2.00% Senior Notes due 2018	Dec. 31, 2012 4.00% Senior Notes due 2019	Apr. 30, 2012 4.00% Senior Notes due 2019	Dec. 31, 2011 4.00% Senior Notes due 2019	Dec. 31, 2012 4.750% Senior Notes due 2021	Dec. 31, 2011 4.750% Senior Notes due 2021	May 31, 2011 4.750% Senior Notes due 2021	Dec. 31, 2012 4.25% senior notes due 2022	Feb. 29, 2012 4.25% senior notes due 2022	Dec. 31, 2011 4.25% senior notes due 2022	Dec. 31, 2012 3.25% Senior Notes due 2022	Dec. 31, 2011 3.25% Senior Notes due 2022	Dec. 31, 2012 6.90% Senior Notes due 2037	Dec. 31, 2011 6.90% Senior Notes due 2037	Dec. 31, 2012 6.59% Senior Notes due 2038	Dec. 31, 2011 6.59% Senior Notes due 2038	Dec. 31, 2012 Mortgage loans and other		Dec. 31, 2011 Mortgage loans and other		Dec. 31, 2012 Unsecured term loan	Dec. 31, 2012 Mortgage loans property loan	Dec. 31, 2011 Mortgage loans property loan
Debt instruments
Total	$ 8,186,315,000	$ 6,180,443,000		$ 540,727,000	$ 455,578,000	$ 0	$ 82,433,000	$ 0	$ 72,950,000	$ 0	$ 200,000,000	$ 269,850,000	$ 269,850,000	$ 130,336,000	[1]	$ 126,875,000	[1]	$ 400,000,000	$ 400,000,000		$ 234,420,000	$ 234,420,000	$ 0	$ 200,000,000	$ 375,000,000	[1]	$ 375,000,000	[1]	$ 0	$ 225,000,000		$ 180,000,000	$ 0	$ 700,000,000	$ 0	$ 600,000,000	$ 600,000,000	$ 0	$ 700,000,000	$ 700,000,000	$ 700,000,000	$ 600,000,000	$ 600,000,000	$ 0	$ 500,000,000	$ 0	$ 52,400,000	$ 52,400,000	$ 22,973,000	$ 22,973,000	$ 2,880,609,000	[2]	$ 2,762,964,000	[2]		$ 23,200,000	$ 14,600,000
Capital lease obligations	142,412,000	143,006,000
Unamortized fair value adjustment	111,623,000	144,923,000
Unamortized commission fees and discounts	(26,704,000)	(39,256,000)
Senior notes payable and other debt	8,413,646,000	6,429,116,000
Interest rate (as a percent)	9.00%		7.125%			9.00%	9.00%	8.25%	8.25%			6.25%	6.25%					3.125%	3.125%	3.125%	6.00%	6.00%	6.50%	6.50%					6.75%	6.75%	6.75%			2.00%	2.00%	4.00%	400.00%	4.00%	4.75%	4.75%	4.75%	4.25%	4.25%	4.25%	3.25%	3.25%	6.90%	6.90%	6.59%	6.59%
Amount outstanding				540,700,000																																																			500,000,000
Principal amount outstanding	$ 8,186,315,000	$ 6,180,443,000		$ 540,727,000	$ 455,578,000	$ 0	$ 82,433,000	$ 0	$ 72,950,000	$ 0	$ 200,000,000	$ 269,850,000	$ 269,850,000	$ 130,336,000	[1]	$ 126,875,000	[1]	$ 400,000,000	$ 400,000,000		$ 234,420,000	$ 234,420,000	$ 0	$ 200,000,000	$ 375,000,000	[1]	$ 375,000,000	[1]	$ 0	$ 225,000,000		$ 180,000,000	$ 0	$ 700,000,000	$ 0	$ 600,000,000	$ 600,000,000	$ 0	$ 700,000,000	$ 700,000,000	$ 700,000,000	$ 600,000,000	$ 600,000,000	$ 0	$ 500,000,000	$ 0	$ 52,400,000	$ 52,400,000	$ 22,973,000	$ 22,973,000	$ 2,880,609,000	[2]	$ 2,762,964,000	[2]		$ 23,200,000	$ 14,600,000

[1] These amounts represent in aggregate the approximate $500.0 million of borrowings outstanding under our unsecured term loan facility. Certain amounts included in the 2015 tranche are in the form of Canadian dollar borrowings.

[2] Excludes debt related to real estate assets classified as held for sale as of December 31, 2012 and 2011, respectively. The total mortgage debt for these properties as of December 31, 2012 and 2011 was $23.2 million and $14.6 million, respectively, and is included in accounts payable and other liabilities on our Consolidated Balance Sheets.