Consolidated Investment Entities - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) fund entity CLO	Dec. 31, 2016 USD ($) fund entity CLO
Variable Interest Entity [Line Items]
Assets of consolidated investment entities	$ 3,176	$ 4,056
Consolidated collateral loan obligations | CLO	4	6
Consolidated funds | fund	14	13
Number of investment funds accounted for as voting interest entity | fund	0
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	$ 1,705	$ 2,495
Number of deconsolidated investment entities | entity	4	2
Parent Issuer
Variable Interest Entity [Line Items]
Assets of consolidated investment entities	$ 442	$ 587