Investments and Fair Value Measurements (Gains (Losses) on Investments) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Available-for-sale:
Available-for-sale securities, Cost	$ 28.2		$ 28.2		$ 18.7
Available-for-sale Securities, Unrealized Gain	1.4		1.4		0.3
Available-for-sale Securities, Unrealized Loss	(1.2)		(1.2)		(1.7)
Available-for-sale securities, Fair Value	28.4		28.4		17.3
Held-to-maturity:
Held-to-maturity securities, Cost	15.9		15.9		15.3
Held-to-maturity Securities, Unrecognized Gain	0.0		0.0		0.0
Held-to-maturity Securities, Unrecognized Loss	0.0		0.0		0.0
Held-to-maturity	15.9		15.9		15.3
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Available-for-sale securities, realized gains	0.5	$ 0.1	1.6	$ 1.0
Available-for-sale securities, realized losses	(0.2)	(0.1)	(1.1)	(0.6)
Available-for-sale securities, realized gains (losses), net	0.3	$ 0.0	0.5	$ 0.4
Equity Securities and Exchange-traded Funds [Member]
Available-for-sale:
Available-for-sale securities, Cost	26.0		26.0		17.4
Available-for-sale Securities, Unrealized Gain	1.3		1.3		0.3
Available-for-sale Securities, Unrealized Loss	(1.2)		(1.2)		(1.6)
Available-for-sale securities, Fair Value	26.1		26.1		16.1
Mutual Funds [Member]
Available-for-sale:
Available-for-sale securities, Cost	2.2		2.2		1.3
Available-for-sale Securities, Unrealized Gain	0.1		0.1		0.0
Available-for-sale Securities, Unrealized Loss	0.0		0.0		(0.1)
Available-for-sale securities, Fair Value	2.3		2.3		1.2
Certificates of Deposit [Member]
Held-to-maturity:
Held-to-maturity securities, Cost	14.1		14.1		15.3
Held-to-maturity Securities, Unrecognized Gain	0.0		0.0		0.0
Held-to-maturity Securities, Unrecognized Loss	0.0		0.0		0.0
Held-to-maturity	14.1		14.1
Convertible Debt Securities [Member]
Held-to-maturity:
Held-to-maturity securities, Cost	1.8		1.8		0.0
Held-to-maturity Securities, Unrecognized Gain	0.0		0.0		0.0
Held-to-maturity Securities, Unrecognized Loss	0.0		0.0		0.0
Held-to-maturity	$ 1.8		$ 1.8		$ 0.0

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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-Publisher FASB
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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

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Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity, expected to be converted to cash, sold or exchanged within one year or the normal operating cycle.

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