SENIOR NOTES PAYABLE AND OTHER DEBT (Details 2) (USD $)	9 Months Ended							9 Months Ended			1 Months Ended		9 Months Ended
	Sep. 30, 2012 Unsecured revolving credit facility	Sep. 30, 2012 Unsecured revolving credit facility Minimum	Sep. 30, 2012 Unsecured revolving credit facility Maximum	Sep. 30, 2012 Letters of credit	Sep. 30, 2012 Swingline loans	Sep. 30, 2012 Alternative currency loans	Sep. 30, 2012 Base rate loans	Sep. 30, 2012 Base rate loans LIBOR	Sep. 30, 2012 Base rate loans Federal funds rate	Sep. 30, 2012 Eurocurrency rate loans	Aug. 31, 2012 Unsecured term loan due 2013	Oct. 31, 2012 Unsecured term loan due 2018	Sep. 30, 2012 Unsecured term loan due 2018 LIBOR
Debt instruments
Current borrowing capacity	$ 2,000,000,000
Maximum borrowing capacity	2,500,000,000			200,000,000	200,000,000	250,000,000
Percentage of line of credit facility for negotiated rate loans	50.00%
Variable interest rate								LIBOR	federal funds rate				LIBOR
Basis spread on variable rate (as a percent)								0.10%	0.50%				1.20%
Percentage of interest rate							0.10%			1.10%
Facility fee (as a percent)	0.175%	0.15%	0.45%
Line of credit facility optional extension period			1 year
Amount outstanding	704,800,000
Letters of credit outstanding	5,900,000
Remaining borrowing capacity	1,290,000,000
Principal amount prepaid											200,000,000
Unsecured term loan												$ 180,000,000