Indebtedness and Derivative Financial Instruments (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Debt Maturity and Other
2014	$ 2,072,529,000
2015	1,972,833,000
2016	5,005,080,000
2017	3,594,748,000
2018	2,031,818,000
Thereafter	8,886,074,000
Total principal maturities	23,563,082,000
Net unamortized debt premiums	25,449,000
Total mortgages and other indebtedness	23,588,531,000	23,113,007,000
Cash paid for interest	1,142,201,000	1,122,223,000	979,436,000
Derivative financial instruments
Unamortized loss of benefits from treasury and interest rate hedge agreements	67,500,000	78,000,000
Amount expected to be reclassified from accumulated other comprehensive loss to earnings within the next year	10,400,000
Fair value of debt
Carrying value of fixed-rate mortgages and unsecured indebtedness	21,800,000,000	21,000,000,000
Fair value of fixed-rate mortgages and unsecured indebtedness	23,297,000,000	23,373,000,000
Weighted average discount rates assumed in calculation of fair value for fixed-rate mortgages (as a percent)	3.07%	3.24%
Interest rate swap
Derivative financial instruments
Notional Amount	491,600,000
Fixed rate swap agreements, weighted average fixed pay rate (as a percent)	3.13%
Fixed rate swap agreements, weighted average variable receive rate (as a percent)	2.00%
Interest rate cap
Derivative financial instruments
Notional Amount	$ 248,300,000