Employee Benefits, Defined Benefit Plans Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
VEBA Postretirement Medical Obligations
Accrued annual contribution to VEBAs	$ 11.5	$ 20.0
Union VEBA
VEBA Postretirement Medical Obligations
Accrued annual contribution to VEBAs	17.1
Maximum contribution threshold	12.8
Accrued Veba contingent contribution - total	11.5
Salaried VEBA
VEBA Postretirement Medical Obligations
Accrued annual contribution to VEBAs	2.9
Maximum contribution threshold	2.9
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
VEBA Postretirement Medical Obligations
Deferred Compensation Plan Assets	$ 8.6	$ 8.2