Debt - Summary of Obligations (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term debt	$ 1,223.0	$ 1,296.4
Less current portion of debt	0.0	(61.9)
Total long-term debt	$ 1,223.0	1,234.5
Stated interest rate (in hundredths)	2.00%
Interest payments made	$ 65.7	66.0
Senior Notes
Debt Instrument [Line Items]
Long-term debt	0.0	61.9
Interest payments made	$ 3.3	3.6
Senior Notes \| Senior Notes Due 2015
Debt Instrument [Line Items]
Long-term debt		$ 61.9
Stated interest rate (in hundredths)	5.375%	5.375%
Maturity date	Nov. 01, 2015	Nov. 01, 2015
Convertible Senior Notes Due 2017
Debt Instrument [Line Items]
Long-term debt	$ 333.5	$ 345.0
Stated interest rate (in hundredths)	5.00%	5.00%
Maturity date	May 01, 2017	May 01, 2017
Interest payments made	$ 17.3	$ 17.3
Convertible Senior Notes - due April 2020
Debt Instrument [Line Items]
Long-term debt	$ 500.0	$ 500.0
Stated interest rate (in hundredths)	2.00%	2.00%
Maturity date	Apr. 01, 2020	Apr. 01, 2020
Interest payments made	$ 10.0	$ 10.0
Convertible Junior Subordinated Debentures Due 2063
Debt Instrument [Line Items]
Long-term debt	$ 389.5	$ 389.5
Stated interest rate (in hundredths)	9.00%	9.00%
Maturity date	Apr. 01, 2063	Apr. 01, 2063
Interest payments made	$ 35.1	$ 35.1

Contractual interest rate for funds borrowed, under the debt agreement.

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-Name Accounting Standards Codification
-Topic 210
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