Borrowing Arrangements (Summary of Senior Notes Payable and Other Debt) (Details) (USD $)																																																																				12 Months Ended		2 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Unsecured revolving credit facilities	Dec. 31, 2012 Unsecured revolving credit facilities	Dec. 31, 2013 6.25% Senior Notes due 2013	Feb. 28, 2013 6.25% Senior Notes due 2013	Dec. 31, 2012 6.25% Senior Notes due 2013	Dec. 31, 2013 Unsecured term loan due 2015		Dec. 31, 2012 Unsecured term loan due 2015		Dec. 31, 2013 3.125% Senior Notes due 2015	Dec. 31, 2012 3.125% Senior Notes due 2015	Dec. 31, 2013 6% Senior Notes due 2015	Dec. 31, 2012 6% Senior Notes due 2015	Dec. 31, 2013 1.55% Senior Notes due 2016	Sep. 30, 2013 1.55% Senior Notes due 2016	Dec. 31, 2012 1.55% Senior Notes due 2016	Dec. 31, 2013 Unsecured term loan due 2017		Dec. 31, 2012 Unsecured term loan due 2017		Dec. 31, 2013 Unsecured term loan due 2018	Dec. 31, 2012 Unsecured term loan due 2018	Dec. 31, 2013 2.00% Senior Notes due 2018	Dec. 31, 2012 2.00% Senior Notes due 2018	Dec. 31, 2013 Unsecured Term Loan Due 2018		Dec. 31, 2012 Unsecured Term Loan Due 2018		Dec. 31, 2013 Unsecured Term Loan Due 2019		Dec. 31, 2012 Unsecured Term Loan Due 2019		Dec. 31, 2013 4.00% Senior Notes due 2019	Dec. 31, 2012 4.00% Senior Notes due 2019	Apr. 30, 2012 4.00% Senior Notes due 2019	Dec. 31, 2013 2.700% Senior Notes due 2020	Mar. 31, 2013 2.700% Senior Notes due 2020	Dec. 31, 2012 2.700% Senior Notes due 2020	Dec. 31, 2013 4.750% Senior Notes due 2021	Dec. 31, 2012 4.750% Senior Notes due 2021	May 31, 2011 4.750% Senior Notes due 2021	Dec. 31, 2013 4.25% Senior Notes due 2022	Dec. 31, 2012 4.25% Senior Notes due 2022	Feb. 29, 2012 4.25% Senior Notes due 2022	Dec. 31, 2013 3.25% Senior Notes due 2022	Dec. 31, 2012 3.25% Senior Notes due 2022	Aug. 31, 2012 3.25% Senior Notes due 2022	Dec. 31, 2013 6.90% Senior Notes due 2037	Dec. 31, 2012 6.90% Senior Notes due 2037	Dec. 31, 2013 6.59% Senior Notes due 2038	Dec. 31, 2012 6.59% Senior Notes due 2038	Dec. 31, 2013 5.45% Senior Notes due 2043	Mar. 31, 2013 5.45% Senior Notes due 2043	Dec. 31, 2012 5.45% Senior Notes due 2043	Dec. 31, 2013 5.70% Senior Notes due 2043	Sep. 30, 2013 5.70% Senior Notes due 2043	Dec. 31, 2012 5.70% Senior Notes due 2043	Dec. 31, 2013 Mortgage loans and other		Dec. 31, 2012 Mortgage loans and other		Dec. 31, 2013 Unsecured term loan	Dec. 31, 2012 Unsecured term loan	Dec. 31, 2013 Mortgage loans held for sale	Dec. 31, 2012 Mortgage loans held for sale	Dec. 31, 2013 Mortgage loans	Dec. 31, 2012 Mortgage loans	Feb. 17, 2014 Mortgage loans Subsequent Event [Member]
Debt instruments
Principal amount outstanding	$ 9,320,477,000	$ 8,186,315,000	$ 376,343,000	$ 540,727,000	$ 0		$ 269,850,000	$ 0	[1]	$ 130,336,000	[1]	$ 400,000,000	$ 400,000,000	$ 234,420,000	$ 234,420,000	$ 550,000,000		$ 0	$ 0	[1]	$ 375,000,000	[1]	$ 0	$ 180,000,000	$ 700,000,000	$ 700,000,000	$ 200,000,000	[2]	$ 0	[2]	$ 800,702,000	[2]	$ 0	[2]	$ 600,000,000	$ 600,000,000		$ 500,000,000		$ 0	$ 700,000,000	$ 700,000,000		$ 600,000,000	$ 600,000,000		$ 500,000,000	$ 500,000,000		$ 52,400,000	$ 52,400,000	$ 22,973,000	$ 22,973,000	$ 258,750,000		$ 0	$ 300,000,000		$ 0	$ 2,524,889,000	[3],[4]	$ 2,880,609,000	[3],[4]			$ 13,100,000	$ 23,200,000
Interest rate (as a percent)					6.25%	6.25%	6.25%					3.125%	3.125%	6.00%	6.00%	1.55%	1.55%	1.55%							2.00%	2.00%									4.00%	4.00%	4.00%	2.70%	2.70%	2.70%	4.75%	4.75%	4.75%	4.25%	4.25%	4.25%	3.25%	3.25%	3.25%	6.90%	6.90%	6.59%	6.59%	5.45%	5.45%	5.45%	5.70%	5.70%	5.70%
Capital lease obligations	0	142,412,000
Unamortized fair value adjustment	69,611,000	111,623,000
Unamortized commission fees and discounts	(25,096,000)	(26,704,000)
Senior notes payable and other debt	9,364,992,000	8,413,646,000
Amount outstanding																																																																1,000,000,000	500,000,000
Repayments of secured debt																																																																				$ 493,700,000	$ 344,200,000	$ 42,700,000

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

[2] These amounts represent in aggregate the approximate $1.0 billion of unsecured term loan borrowings under our new unsecured credit facility. Certain amounts included in the 2019 tranche are in the form of Canadian dollar borrowings.

[3] Excludes debt related to real estate assets classified as held for sale as of December 31, 2013 and 2012, respectively. The total mortgage debt for these properties as of December 31, 2013 and 2012 was $13.1 million and $23.2 million, respectively, and is included in accounts payable and other liabilities on our Consolidated Balance Sheets.

[4] Subsequent to December 31, 2013, we repaid in full approximately $42.7 million of the mortgage loans outstanding as of December 31, 2013.