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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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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 the excess of amortized cost basis over fair value of securities that have been in a loss position for less than twelve months for securities categorized neither as held-to-maturity nor trading securities.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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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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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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Investments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Investments
Carrying Value	$ 971.4		$ 922.1
Available-for-sale securities
Book cost basis	209.9		200.9
Gross unrealized gains	473.0		412.5
Gross unrealized losses	(1.0)		(1.9)
Market value	681.9		611.5
Proceeds from sale of investments	94.3	56.0
Gross realized gains	69.1	16.5
Gross realized losses	0.4	1.1
Unrealized losses related to other than temporary investment impairments	0.2	0.3
Other than Temporary impairment
Lower of cost or market valuation adjustments on cost method investments	0.3	0.4
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	15.5		25.7
Total	15.5		25.7
Unrealized losses of investments by the length of time that the securities have in a continuous loss position
Less than 12 months	1.0		1.9
Total	1.0		1.9
Private Equity Funds
Investments
Carrying Value	220.2		231.4
Future capital commitments
Future capital commitments related to private equity fund investments	11.9
Available-for-sale securities
Investments
Carrying Value	681.9		611.5
Available-for-sale securities \| State Street Corporation
Investments
Carrying Value	518.8		436.3
Available-for-sale securities \| Other available-for-sale securities
Investments
Carrying Value	163.1		175.2
Other investments
Investments
Carrying Value	289.5		310.6
Other investments \| Trading securities
Investments
Carrying Value	52.6		46.8
Other investments \| Held-to-maturity
Investments
Carrying Value			14.9
Other investments \| Cost method, private equity and other investments
Investments
Carrying Value	$ 236.9		$ 248.9