Net Loss Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator
Net loss	$ (200.6)	$ (43.2)
Distributed and allocated undistributed net (loss) earnings to non-vested restricted stockholders	(0.2)	0.1
Distributed and allocated undistributed net loss	(200.8)	(43.1)
Distributed net loss - dividends paid	(26.3)	(31.0)
Allocation of undistributed net loss to common stockholders	$ (227.1)	$ (74.1)
Denominator
Weighted average number of common shares outstanding - basic (in shares)	165.3	193.4
Basic net earnings per common share:
Distributed net earnings (in dollars per share)	$ 0.16	$ 0.16
Allocated undistributed net loss to common stockholders (in dollars per share)	(1.37)	(0.38)
Net loss per common share - basic (in dollars per share)	$ (1.21)	$ (0.22)
Numerator
Distributed and allocated undistributed net loss	$ (200.8)	$ (43.1)
Add: Allocated undistributed net earnings to unvested restricted stockholders	0.0	0.0
Less: Undistributed net earnings reallocated to non-vested restricted stockholders	0.0	0.0
Net loss available to common stockholders - diluted	$ (200.8)	$ (43.1)
Denominator
Weighted average number of common shares outstanding - basic (in shares)	165.3	193.4
Effect of contingently issuable shares (in shares)	0.0	0.8
Effect of unvested restricted stock units (in shares)	0.0	0.9
Weighted average number of common shares outstanding - diluted under two-class	165.3	195.1
Effect of unvested restricted stock - participating security (in shares)	0.0	0.6
Weighted average number of common shares outstanding - diluted under treasury stock	165.3	195.7
Diluted net loss per common share (in dollars per share)	$ (1.21)	$ (0.22)