Investment Securities (Restrictions on Redemption Frequency and Advance Notice Requirements) (Details) - Hedge funds $ in Millions	Dec. 31, 2016 USD ($) fund
Investment securities
Number of Investments Held | fund	5
Trading Securities, Other	$ 59.8
Distributions from inactive hedge funds	1.0
Outstanding redemptions	2.4
30-59 days notice
Investment securities
Trading Securities, Other	37.5
60-89 days notice
Investment securities
Trading Securities, Other	19.9
90-119 days notice
Investment securities
Trading Securities, Other	2.4
Monthly
Investment securities
Trading Securities, Other	0.0
Monthly | 30-59 days notice
Investment securities
Trading Securities, Other	0.0
Monthly | 60-89 days notice
Investment securities
Trading Securities, Other	0.0
Monthly | 90-119 days notice
Investment securities
Trading Securities, Other	0.0
Quarterly
Investment securities
Trading Securities, Other	15.9
Quarterly | 30-59 days notice
Investment securities
Trading Securities, Other	15.9
Quarterly | 60-89 days notice
Investment securities
Trading Securities, Other	0.0
Quarterly | 90-119 days notice
Investment securities
Trading Securities, Other	0.0
Semi-annual
Investment securities
Trading Securities, Other	41.5
Semi-annual | 30-59 days notice
Investment securities
Trading Securities, Other	21.6
Semi-annual | 60-89 days notice
Investment securities
Trading Securities, Other	19.9
Semi-annual | 90-119 days notice
Investment securities
Trading Securities, Other	$ 0.0
Lock-up period expiring 2018
Investment securities
Number of Investments Held | fund	1
Trading Securities, Other	$ 21.5
Annual
Investment securities
Trading Securities, Other	2.4
Annual | 30-59 days notice
Investment securities
Trading Securities, Other	0.0
Annual | 60-89 days notice
Investment securities
Trading Securities, Other	0.0
Annual | 90-119 days notice
Investment securities
Trading Securities, Other	$ 2.4