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Fair Value Measurements - Schedule of Changes in Level 3 Assets (Details) - Other Investments - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period		$ 133.4	$ 139.5	$ 134.2	$ 131.8
Net gains/losses	[1]	2.0	2.7	0.2	13.7
Purchases and issuances		5.9	3.7	12.1	10.5
Settlements and reductions		(8.9)	(8.2)	(20.6)	(18.3)
Net transfers in and/or out of Level 3		0.0	0.0	6.5	0.0
Balance, end of period		132.4	137.7	132.4	137.7
Net unrealized gains/losses relating to instruments still held at the reporting date	[1]	$ 6.0	$ 4.4	$ 9.6	$ 17.1
[1] Gains and losses on Other investments are recorded in Investment and other income.

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- Definition

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Settlements And Reductions

+ References

No definition available.

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- Definition

Fair Value, Measurement with Unobservable Inputs Reconciliation Recurring Basis, Asset, Purchases And Issuances

+ References

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- Definition

Amount of unrealized (holding) gain (loss) which is included in the statement of income (or changes in net assets) related to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 820



-SubTopic 10



-Section 50



-Paragraph 2



-Subparagraph (d)



-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 820



-SubTopic 10



-Section 50



-Paragraph 2



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- Definition

Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 820



-SubTopic 10



-Section 50



-Paragraph 2



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