Stock Option and Incentive Plan (Restricted Stock) (Narrative) (Details) (USD $)	12 Months Ended			48 Months Ended		12 Months Ended				12 Months Ended						0 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Feb. 01, 2013	Dec. 31, 2012 Restricted Stock [Member]	Feb. 01, 2013 Restricted Stock [Member]	Dec. 31, 2011 Restricted Stock [Member]	Dec. 31, 2010 Restricted Stock [Member]	Dec. 31, 2012 LTIP Units [Member]	Dec. 31, 2011 LTIP Units [Member]	Dec. 31, 2010 LTIP Units [Member]	Dec. 31, 2011 OPP Units Two Thousand And Eight [Member] Y	Dec. 31, 2012 LTIPs And Restricted Stock [Member] VestingInstallments	Dec. 31, 2012 LTIPs and OPP Awards [Member]	Jan. 25, 2012 OPP Units 2012 [Member] Y	Dec. 31, 2012 OPP Units 2012 [Member]	Dec. 31, 2012 OPP Units 2012 [Member]	Dec. 31, 2012 OPP Units 2012 [Member] SNL Equity REIT [Member]	Dec. 31, 2012 Non Qualified Stock Options [Member]	Dec. 31, 2011 Non Qualified Stock Options [Member]	Dec. 31, 2011 OPP Units 2011 [Member]	Dec. 31, 2012 Unvested 2011 and 2012 OPP Units [Member]	Dec. 31, 2012 Non-Qualified Employee Stock Purchase Plan [Member] D	Dec. 31, 2011 Non-Qualified Employee Stock Purchase Plan [Member]	Dec. 31, 2010 Non-Qualified Employee Stock Purchase Plan [Member]	Dec. 31, 2012 Executive Vice President [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued	151,680,109	148,186,511				20,756	35,087	19,030	69,499
LTIP units issued (in shares)					153,006					174,650	190,067	252,597
Non-qualified stock options issued (in shares)					201,373															186,007	146,844
2012 OPP units issued (in shares)																		400,000				400,000
Employee and director payment per share (in dollars per share)						$ 0.01									$ 0.25
Vesting annual installments														4
Stock-based compensation associated with restricted stock, non-qualified options, LTIP Units, 2008 OPP Units, 2011 OPP Units, and 2012 OPP Units	$ 28,300,000	$ 28,300,000	$ 31,900,000																								$ 2,700,000
TRS measurement (in years)													3			3
Accelerated Compensation Expenses Related To 2008 Opp Units		4,300,000
Accelerated Amount Of Unvested Compensation Expense.				5,800,000
Unrecognized compensation expenses														21,100,000									8,400,000
Weighted-average period (years)																							2 years 6 months 0 days
Value of shares of common stock	1,516,000	1,481,000				2,200,000		1,800,000	4,500,000
Employee's weighted average cost per share (in dollars per share)						$ 107.31		$ 93.40	$ 65.31
Value of LTIP units issued										17,300,000	16,500,000	15,300,000
Per unit fair value weighted-average (in dollars per share)										$ 98.83	$ 86.74	$ 60.49
Expected life assumed to calculate per unit fair value per LTIP unit (years)										5 years 9 months 19 days	5 years 9 months 19 days	5 years 8 months 12 days								5 years 4 months 24 days	6 years 0 months 0 days
Risk-free rate										0.94%	2.22%	2.60%					0.35%			0.92%	2.37%
Expected price volatility										29.10%	30.00%	36.00%					31.00%		30.00%	28.40%	35.00%
Expected dividend rate																				2.90%	3.00%
Value of OPP units																	7,700,000	7,700,000
Method of valuation										Monte Carlo simulation method								The Monte Carlo simulation used a statistical formula underlying the Black-Scholes and binomial formulas and such simulation was run approximately 100,000 times.		The non-qualified stock options granted during the nine months ended September 30, 2012 had a weighted-average fair value on the date of grant of $19.50 per option, which was computed using the Black-Scholes option-pricing model utilizing the following weighted-average assumptions: an expected life of 5.4 years, a risk-free interest rate of 0.92%, an expected price volatility of 28.4% and an expected dividend yield of 2.9%.
Estimated dividend payments (in dollars per share)																	7.28
Weighted-average grant date fair value (in dollars per share)	$ 107.23	$ 92.71	$ 0																	$ 19.50	$ 24.67
Weighted-average exercise price (in dollars per share)																				$ 107.23	$ 92.71
Exercisable, Weighted Average Exercise Price		$ 54.32	$ 32.65
Maximum Common Stock available for issuance																								250,000
Employee Common Stock options, percent of average closing price																								85.00%
Number Of Days Used In Calculation, Average Closing Prices Of Common Stock																								10
Shares issued																								7,406	6,356	9,131
Shares issued, weighted-average purchase price per share																								$ 86.52	$ 80.13	$ 61.61
Number Exercisable at 12/31/2010		13,633	324,938
Total intrinsic value of the outstanding and exercisable stock options	$ 700,000