CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (PARENTHETICAL) - USD ($) shares in Millions, $ in Millions	1 Months Ended			3 Months Ended
	Jun. 30, 2017	Feb. 28, 2017	Feb. 28, 2015	Jun. 30, 2017
2017 Junior Subordinated Convertible Debt
Proceeds from issuance of senior subordinated convertible debentures, net of issuance costs		$ 567.7
2017 Junior Subordinated Convertible Debt | Long-term Debt
Proceeds from issuance of senior subordinated convertible debentures, net of issuance costs	$ 111.3
2007 Junior Subordinated Convertible Debt | Long-term Debt
Stock issued during period, shares, conversion of convertible securities	3.2	12.0		0.5
Extinguishment of debt	$ 111.3	$ 431.3	$ 575.0