Contingencies (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Commitments and Contingencies
Maximum liability under indemnity in connection with liquidation of an investment acquired	$ 23.0
Letters of Credit
Commitments and Contingencies
Commitments	683.4	733.5
Standby letters of credit, included within letters of credit
Commitments and Contingencies
Commitments	577.9	617.3
Commercial letters of credit, including within letters of credit
Commitments and Contingencies
Commitments	$ 105.5	$ 116.2