Commitments and Contingencies Loss Contingency (Details) CAD in Millions, $ in Millions		1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 12, 2014 CAD	Dec. 31, 2009 CAD	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 1990 USD ($)
Loss Contingencies [Line Items]
Loss Contingency Accrual, Period Increase (Decrease)			$ 50.0
Guarantor Obligations, Current Carrying Value			48.8		$ 31.7
Guarantees
Letter of credit provided to entity | CAD		CAD 10
Litigation and Other Disputes
Accrued liabilities, litigations and disputes			26.0		27.7
Loss contingency, possible loss, portion not accrued			$ 136.0
Loss Contingency Accrual, Provision					50.0
Kaiser Tax, Civil and Labor Indemnity Reserve [Member]
Loss Contingencies [Line Items]
Equity interest sold (as a percent)			68.00%
Environmental matters Lowry [Member]
Environmental
Environmental remediation expense, pretax charge						$ 30.0
Environmental remediation threshold, assumed remediation cost			$ 120.0
Inflation rate assumption, future costs (as a percent)			2.50%
Risk free rate of return assumption (as a percent)			2.71%
Site contingency, accrual, present value			$ 3.0
Site contingency, accrual, undiscounted amount			6.0
David Hughes and 631992 Ontario Inc [Member]
Litigation and Other Disputes
Loss contingency, damages sought | CAD	CAD 1,400
Cervejarias Kaiser Brasil S.A. [Member]
Loss Contingencies [Line Items]
Gain (loss) discontinued operations			(0.6)	$ (0.5)
Other Noncurrent Liabilities [Member] | Canada [Member]
Loss Contingencies [Line Items]
Guarantor Obligations, Current Carrying Value			4.5		$ 4.4
Maximum [Member]
Litigation and Other Disputes
Loss Contingency, Estimate of Possible Loss			142.0
Maximum [Member] | Kaiser purchased tax credits indemnity reserve, category two
Litigation and Other Disputes
Loss Contingency, Estimate of Possible Loss			112.1
Maximum [Member] | Kaiser Tax, Civil and Labor Indemnity Reserve [Member]
Litigation and Other Disputes
Loss Contingency, Estimate of Possible Loss			$ 68.0