Commitments and Contingencies - Guarantees and Indemnifications Narrative (Details)						0 Months Ended
	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2014 Commitments to fund certain limited partnerships or subsidiaries [Member] USD ($)	Dec. 31, 2013 Commitments to fund certain limited partnerships or subsidiaries [Member] USD ($)	Jun. 15, 2011 Commitments to fund certain limited partnerships or subsidiaries [Member] Subsidiaries [Member] Term Credit Agreement [Member] USD ($)	Mar. 20, 2012 Commitments to fund certain limited partnerships or subsidiaries [Member] Subsidiaries [Member] Five-Year Agreement [Member]	Mar. 20, 2012 Commitments to fund certain limited partnerships or subsidiaries [Member] Subsidiaries [Member] Five-Year Agreement [Member] USD ($)	Oct. 15, 2010 Commitments to fund certain limited partnerships or subsidiaries [Member] Subsidiaries [Member] Euro Facility Agreement [Member] EUR (€)
Other Commitments [Line Items]
Maximum potential funding under commitments	$ 112,000,000	$ 98,000,000	$ 14,000,000	$ 34,000,000	$ 450,000,000		$ 400,000,000	€ 650,000,000
Term of credit agreement						5 years