Indebtedness (Unsecured Lines of Credit) (Details) (Unsecured Line of Credit DRLP [Member], USD $)	12 Months Ended	9 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2012
Maximum Capacity	$ 1,200,000,000	850,000,000
Maturity date	Jan. 01, 2019
Line of credit balance	106,000,000		285,000,000
Line of Credit Facility, Increase, Additional Borrowings	400,000,000
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,600,000,000
Line of Credit Facility, Covenant Compliance	we were in compliance with all covenants under this line of credit.
Current Market rate of Unsecured lines of Credit	1.42%
London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Description of Variable Rate Basis	LIBOR	LIBOR
Debt Instrument, Basis Spread on Variable Rate	1.05%	1.25%
Line of Credit Facility, Interest Rate at Period End	1.22%