Changes in Capital Structure - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	6 Months Ended		12 Months Ended
	Jul. 31, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Apr. 27, 2017	Jun. 13, 2016	May 24, 2016
Capital Structure
Common stock, shares authorized (in shares)		500,000,000	500,000,000	500,000,000	500,000,000
Redemption of shares (as percent)		100.00%		100.00%
Increase in shares available for issuance under the Amended and Restated Long-term Incentive Plan						3,000,000
Shares of treasury stock available for issuance under the ESPP			3,385,289
Shares issued under ESPP			282,530
Increase in Shares Available for Issuance, LTIP						3,000,000
Issued
Capital Structure
Shares issued under ESPP			0
Issued | Subsequent Event
Capital Structure
Shares issued under ESPP	278,240
Treasury
Capital Structure
Shares issued under ESPP			282,530
Convertible Preferred Stock
Capital Structure
Redemption of shares (as percent)							100.00%	100.00%
Preferred shares repurchased (in shares)								$ 344.5
Preferred stock, dividend rate amended (as percent)				2.822%	2.822%
Repurchase of outstanding shares		$ 226.0
Gain on redemption		$ 78.0
Carrying value of preferred stock at time of redemption Attributable to Parent							$ 304.0