Investments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Investments
Carrying Value	$ 778.0		$ 881.3
Available-for-sale securities
Book cost basis	162.3		166.9
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	420.1		487.5
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	(0.6)		(0.4)
Market value	581.8		654.0
Proceeds from sale of investments	69.0	94.3
Gross realized gains	46.1	69.1
Gross realized losses	0.1	0.4
Unrealized losses related to other than temporary investment impairments	0.1	0.2
Other than Temporary impairment
Lower of cost or market valuation adjustments on cost method investments	0.3	0.3
Common Stock
Fair value of investments by the length of time that the securities have been in a continuous loss position
Less than 12 months	13.9		5.9
Total	13.9		5.9
Unrealized losses of investments by the length of time that the securities have in a continuous loss position
Less than 12 months	0.6	0.4
Total	0.6	0.4
Cost method and other investments
Investments
Carrying Value	15.4		15.7
Future capital commitments
Investment Income, Dividend	33.2
Private Equity Funds
Investments
Carrying Value	150.9		167.3
Future capital commitments
Future capital commitments related to private equity fund investments	6.7
Available-for-sale securities
Investments
Carrying Value	581.8		654.0
Deferred Tax Liabilities, Other	173.6		201.1
Available-for-sale securities \| State Street Corporation
Investments
Carrying Value	446.8		515.5
Available-for-sale securities \| Other available-for-sale securities
Investments
Carrying Value	135.0		138.5
Other investments
Investments
Carrying Value	196.2		227.3
Other investments \| Trading securities
Investments
Carrying Value	29.9		44.3
Other investments \| Cost method and other investments
Investments
Carrying Value	$ 166.3		$ 183.0

Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments

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Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments

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Represents the entity's future capital commitments related to a limited partner investment.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount of unrealized loss on securities classified as available-for-sale.

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This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

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Amount of unrealized loss on investments in available-for-sale securities that have been in a loss position for less than twelve months.

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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 not separately disclosed.

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Amount of dividend income on nonoperating securities.

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The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle).

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The amount of other than temporary impairment losses on investments in debt and equity securities categorized as Available-for-sale which have been recognized in earnings during the period. Such impairment losses consist of other than temporary impairments (OTTI) on equity securities, credit losses on investments in debt securities, and when the entity intends to sell an impaired debt security or it is more likely than not that the entity will be required to sell the impaired debt security before recovery of its amortized cost basis.

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