Variable Interest Entities - Number of FG VIE's Consolidated (Details) - Variable Interest Entity, Primary Beneficiary [Member] - Entity	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Number of FG VIEs Consolidated [Roll Forward]
Number of FG VIE's consolidated, beginning of period	32	32
Number of FG VIE's consolidated	0	1
Number of FG VIE's deconsolidated	(1)	(2)
Number of FG VIE's consolidated, end of period	31	31