Investments (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Investment [Line Items]
Carrying Value	$ 377.4	$ 418.2
Cost method, private equity and other investments
Investment [Line Items]
Carrying Value	16.8	16.0
Available-for-sale securities
Investment [Line Items]
Carrying Value	180.5	219.5
Available-for-sale securities | State Street Corporation
Investment [Line Items]
Carrying Value	169.6	144.8
Available-for-sale securities | Other available-for-sale securities
Investment [Line Items]
Carrying Value	10.9	74.7
Other investments
Investment [Line Items]
Carrying Value	196.9	198.7
Other investments | Trading securities
Investment [Line Items]
Carrying Value	7.9	14.8
Other investments | Seed Capital Investments, at fair value
Investment [Line Items]
Carrying Value	61.0	50.7
Other investments | Cost method, private equity and other investments
Investment [Line Items]
Carrying Value	$ 128.0	$ 133.2