Employee Benefits, Defined Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
VEBAs
VEBA Postretirement Medical Obligations
Cash flow in determining VEBA obligation	$ 20.0
VEBAs | Maximum
VEBA Postretirement Medical Obligations
Administrative expenses of the VEBAs obligation	0.3
Union VEBA
VEBA Postretirement Medical Obligations
Number of trustees	4
Percent allocation of total contribution between VEBAs	85.50%
Union VEBA | Company Appointed
VEBA Postretirement Medical Obligations
Number of trustees	2
Salaried VEBA
VEBA Postretirement Medical Obligations
Percent allocation of total contribution between VEBAs	14.50%
Variable cash contribution | VEBAs
VEBA Postretirement Medical Obligations
Annual VEBA contribution paid	20.0
Variable cash contribution | VEBAs | Maximum
VEBA Postretirement Medical Obligations
Variable cash contribution obligation to VEBAs	$ 20.0
Variable cash contribution | VEBAs | Annual Cash Flows up to $20 Million
VEBA Postretirement Medical Obligations
Postretirement medical plan contribution obligation percentage	10.00%
Variable cash contribution | VEBAs | Annual Cash Flows in Excess of $20 Million
VEBA Postretirement Medical Obligations
Postretirement medical plan contribution obligation percentage	20.00%