Benefit Plans Benefit Plans - Change in Plan Assets Unobservable Inputs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Document Period End Date	Dec. 31, 2016
Pension Benefits | Level 3
Defined Benefit Plan Disclosure [Line Items]
Balance, January 1	$ 53.3	$ 54.1
Dispositions	(8.3)	(6.1)
Realized and unrealized gain, net	2.5	5.3
Balance, December 31	278.0	53.3
Acquisition	$ 230.5	$ 0.0