Stock Option And Incentive Plan (Restricted Stock) (Narrative) (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Shares issued	150,794,602		150,794,602		148,186,511
Value of shares of common stock	$ 1,507,000		$ 1,507,000		$ 1,481,000
Stock-based compensation expense associated with restricted stock, LTIP Units, 2008 OPP Units, 2011 OPP Units and 2012 OPP Units	6,400,000	5,600,000	17,400,000	17,200,000
Accelerated Compensation Expenses Related To 2008 Opp Units				4,300,000
Executive Vice President [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Stock-based compensation expense associated with restricted stock, LTIP Units, 2008 OPP Units, 2011 OPP Units and 2012 OPP Units			2,700,000
OPP Units 2012 [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Opp Units Value	7,700,000		7,700,000
Method of valuation			The Monte Carlo simulation used a statistical formula underlying the Black-Scholes and binomial formulas and such simulation was run approximately 100,000 times.
Expected price volatility			31.00%
Risk-free rate			0.35%
Estimated dividend payments, per share			7.28
2012 OPP Units issued	400,000		400,000
OPP Units 2012 [Member] | SNL Equity REIT [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Expected price volatility			30.00%
Non Qualified Stock Options [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Method of valuation			The non-qualified stock options granted during the six months ended June 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%.
Expected price volatility			28.40%
Risk-free rate			0.92%
Non-qualified stock options issued	186,007		186,007
Weighted-average grant date fair value			$ 19.50
Expected life assumed to calculate per unit fair value per LTIP unit (years)			5 years 4 months
Expected dividend rate			2.90%
Weighted-average exercise price			$ 107.23
LTIP Units [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Expected price volatility			29.10%
Risk-free rate			0.94%
LTIP Units issued	174,650		174,650
Expected life assumed to calculate per unit fair value per LTIP unit (years)			5 years 9 months 18 days
Value of LTIP Units issued			17,300,000
Per unit fair value weighted-average	$ 98.83		$ 98.83
LTIPs And Restricted Stock [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Vesting annual installments			4
Unrecognized compensation expenses	29,400,000		29,400,000
Unvested 2011 and 2012 OPP Units [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Unrecognized compensation expenses	10,400,000		10,400,000
Weighted-average period (years)			2 years 9 months 18 days
Restricted Stock [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Shares issued	20,756		20,756
Employee and director payment per share			$ 0.01
Value of shares of common stock	$ 2,200,000		$ 2,200,000
Employee's weighted average cost per share	$ 107.31		$ 107.31
LTIPs and OPP Awards [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Employee and director payment per share			$ 0.25