Accounting Policies Real Estate and Depreciation, In-place Leases (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2015 Leases, Acquired-in-Place [Member]	Dec. 31, 2014 Leases, Acquired-in-Place [Member]	Dec. 31, 2013 Leases, Acquired-in-Place [Member]	Dec. 31, 2012 Leases, Acquired-in-Place [Member]	Dec. 31, 2011 Leases, Acquired-in-Place [Member]	Dec. 31, 2011 Leases, Acquired-in-Place, Tenant Origination Costs [Member]	Dec. 31, 2010 Leases, Acquired-in-Place, Tenant Origination Costs [Member]	Dec. 31, 2011 Leases, Acquired-in-Place, Leasing Commissions and Absorbtion Costs [Member]	Dec. 31, 2010 Leases, Acquired-in-Place, Leasing Commissions and Absorbtion Costs [Member]	Dec. 31, 2011 Leases, Acquired-in-Place, Net Lease Intangible Assets [Member]	Dec. 31, 2010 Leases, Acquired-in-Place, Net Lease Intangible Assets [Member]	Dec. 31, 2011 Leases, Acquired-in-Place, Below-Market Ground Lease [Member]	Dec. 31, 2010 Leases, Acquired-in-Place, Below-Market Ground Lease [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross Carrying Value									$ 55.7	$ 40.5	$ 86.7	$ 58.0	$ 14.5	$ 7.6	$ 12.1	$ 12.1
Finite-Lived Intangible Assets, Accumulated Amortization									25.5	19.6	34.8	24.9	5.7	4.3	0.8	0.6
Finite-Lived Intangible Assets, Net									30.2	20.9	51.9	33.1	8.8	3.3	11.3	11.5
Finite-lived Intangible Liabilities, Net Lease, Gross	32.0	29.8
Finite-lived Intangible Liabilities, Net Lease, Accumulated Amortization	19.3	16.1
Finite-lived Intangible Liabilities, Net Lease, Net	12.7	13.7
Amortization	15.4	7.7	7.3
2012								19.4
2013							15.8
2014						13.7
2015					11.3
2016				$ 8.2