Fair Value Measurements (Investments in Joint Ventures) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unconsolidated investments	$ 82.0	$ 81.1
Equity Method Investments [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value option, number of investments	2	2
FV Option	47.5	47.6
Equity Method Investments [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
The funds, unfunded commitments	5.4
Funds	34.5	33.5
Recurring [Member] | Level 3 [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unconsolidated investments	$ 82.0	$ 81.1