Fair Value Measurement - Accumulated Derivative Instruments (Loss) Gain (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cumulative Changes in Derivative Net Gain (Loss) [Roll Forward]
Balance at beginning of period	$ (13.5)	$ (12.5)	$ (1.3)
Reclassification to earnings	15.0	11.7	0.8
Current period change in fair value	6.0	(12.7)	(12.0)
Balance at end of period	7.5	$ (13.5)	$ (12.5)
Expected reclassification of pre-tax losses in the next twelve months from ACOL to earnings	$ (6.9)