Shareholders' Deficit (Details) - USD ($) $ in Millions	6 Months Ended	39 Months Ended
	Jun. 30, 2017	Jun. 30, 2017	Feb. 28, 2017
Non-recourse notes due 2029
Share Repurchase Program
Payment of principal	$ 64.4	$ 71.3
2017 Capital Return Plan
Share Repurchase Program
Amount approved under share repurchase program			$ 150.0
2017 Capital Return Plan | Non-recourse notes due 2029
Share Repurchase Program
Payment of principal	$ 50.0