Fair Value Measurements - Level 3 Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Balance at the beginning of the period	$ 1.6	$ 7.0	$ 3.5
Purchases	8.1	3.9	15.6
Settlements	(6.6)	(9.3)	(12.1)
Balance at the end of the period	$ 3.1	$ 1.6	$ 7.0