Convertible Securities (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Schedule of Carrying Value of Convertible Securities

The carrying value and principal amount at maturity of the junior convertible securities were as follows:

	December 31, 2016				December 31, 2017
	Carrying Value		Principal Amount at Maturity		Carrying Value		Principal Amount at Maturity
Junior convertible securities(1)	$	307.5	$	430.8	$	309.9	$	430.8

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⁽¹⁾  The carrying value is accreted to the principal amount at maturity over a remaining life of 20 years.