Investments (Details 3) - USD ($) shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale securities
Investments	$ 377.4	$ 418.2
Proceeds from sale of investments	61.2	303.5	$ 278.9
Gross realized gains	6.1	175.1	184.0
Gross realized losses	3.8	6.7	2.6
Unrealized losses related to other than temporary investment impairments	0.2	4.8	2.3
Seed capital investments cash collateral	8.4	10.8
Cost-method Investments, Realized Gain (Loss)			103.6
Other-than temporary impairment
Lower of cost or market valuation adjustments on cost method investments	0.0	0.2	2.2
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	115.0	120.9
Cost method, private equity and other investments
Available-for-sale securities
Investments	$ 16.8	16.0
Cash dividend received			$ 33.2
State Street Corporation
Available-for-sale securities
Investment in available-for-sale equity securities, number of shares held	2.2
Private equity funds
Available-for-sale securities
Investments	$ 111.2	117.2
Future capital commitments related to private equity fund investments	3.8
Available-for-sale securities
Available-for-sale securities
Investments	180.5	219.5
Deferred Tax Liabilities, Other	62.2	54.8
Available-for-sale securities \| State Street Corporation
Available-for-sale securities
Investments	169.6	144.8
Other investments
Available-for-sale securities
Investments	196.9	198.7
Other investments \| Seed Capital Investments
Available-for-sale securities
Investments	61.0	50.7
Other investments \| Cost method, private equity and other investments
Available-for-sale securities
Investments	$ 128.0	$ 133.2

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Cash collateral deposited with a broker for securities sold short

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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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The total amount of proceeds received for the sale of securities, categorized neither as held-to-maturity nor trading securities, during the reporting period.

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This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the cost method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

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Amount of deferred tax liability attributable to taxable temporary differences classified as other.

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The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

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