Equity (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of restricted stock
Compensation expense related to long-term compensation plans, restricted stock and stock options capitalized to assets	$ 4,100,000	$ 3,400,000	$ 2,200,000
Stock options
Stock based compensation
Options expiration period	10 years
Period of commencement of option vesting, from date of grant	1 year
Weighted average assumptions used for estimation of fair value of each stock option
Dividend yield (as a percent)	2.00%	2.00%	2.00%
Expected life of option	3 years 8 months 12 days	4 years 2 months 12 days	5 years 1 month 6 days
Risk-free interest rate (as a percent)	0.46%	1.00%	2.09%
Expected stock price volatility (as a percent)	37.40%	47.98%	50.07%
Weighted average fair value of awards granted during the period	6,602,967	4,647,554	4,333,281
Options Outstanding
Balance at beginning of year (in shares)	1,277,200	1,353,002	1,324,221
Granted (in shares)	361,331	212,400	180,250
Exercised (in shares)	(382,612)	(243,901)	(109,636)
Lapsed or cancelled (in shares)	(54,919)	(44,301)	(41,833)
Balance at end of period (in shares)	1,201,000	1,277,200	1,353,002
Options exercisable at end of period (in shares)	479,913	644,429	631,224
Weighted Average Exercise Price
Balance at beginning of year (in dollars per share)	$ 63.37	$ 58.85	$ 56.74
Granted (in dollars per share)	$ 75.36	$ 66.42	$ 62.00
Exercised (in dollars per share)	$ 36.65	$ 40.48	$ 31.49
Lapsed or cancelled (in dollars per share)	$ 72.99	$ 65.89	$ 77.33
Balance at end of period (in dollars per share)	$ 75.05	$ 63.37	$ 58.85
Options exercisable at end of period (in dollars per share)	$ 86.85	$ 72.31	$ 69.42
Exercise price of options granted, low end of the range (in dollars per share)	$ 20.67
Exercise price of options granted, high end of the range (in dollars per share)	$ 137.18
Remaining weighted average contractual life of the options outstanding	4 years 25 days
Remaining weighted average contractual life of the options exercisable	4 years 3 months 22 days
Share-based compensation, additional disclosures
Compensation expense	5,100,000	4,700,000	4,400,000
Total unrecognized compensation cost related to unvested stock awards	9,100,000
Weighted average period for recognition of compensation cost related to unvested stock awards	3 years
Stock options | Minimum
Stock based compensation
Options vesting period	1 year
Stock options | Maximum
Stock based compensation
Options vesting period	5 years
Restricted Stock Awards
Weighted average assumptions used for estimation of fair value of each stock option
Weighted average fair value of awards granted during the period	7,023,942	21,768,084	28,269,983
Share-based compensation, additional disclosures
Compensation expense	6,930,381	17,365,401	15,327,206
Total unrecognized compensation cost related to unvested stock awards	11,100,000
Weighted average period for recognition of compensation cost related to unvested stock awards	2 years 4 months 24 days
Annual award vesting rate, low end of range (as a percent)	15.00%
Annual award vesting rate, high end of range (as a percent)	35.00%
Summary of restricted stock
Balance at beginning of year (in shares)	2,912,456	2,728,290	2,330,532
Granted (in shares)	92,729	185,333	400,925
Cancelled (in shares)	(200,284)	(1,167)	(3,167)
Balance at end of period (in shares)	2,804,901	2,912,456	2,728,290
Vested during the period (in shares)	408,800	66,299	153,644
Fair value of restricted stock vested during the period	22,400,000	4,300,000	16,600,000
LTIP units
Weighted average assumptions used for estimation of fair value of each stock option
Weighted average fair value of awards granted during the period	$ 8,500,000