Employee Benefits, Defined Benefit Plans Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2015	Sep. 30, 2015	Sep. 30, 2016	Dec. 31, 2015
VEBA Postretirement Medical Obligations
Accrued annual contribution to VEBAs			$ 0.0	$ 19.6
VEBAs
VEBA Postretirement Medical Obligations
Accrued annual contribution to VEBAs				19.5
Union VEBA
VEBA Postretirement Medical Obligations
Accrued annual contribution to VEBAs				16.7
Non-cash loss	$ 307.8
Income tax benefit	$ 184.4	$ 184.4
Accrued Veba contingent contribution - total			$ 29.9
Salaried VEBA
VEBA Postretirement Medical Obligations
Accrued annual contribution to VEBAs				$ 2.8