Employee Benefit Plans Amounts Recognized in the Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation	$ 29.9
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation	35.9
GM Postretirement Cost Sharing Asset, Current	13.3
GM Postretirement Cost Sharing Asset, Noncurrent	259.7	260.2
Total GM Postretirement Cost Sharing Asset	273.0	270.6
Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Amounts Recognized in Balance Sheet	(147.4)	(275.0)
Defined Benefit Plan, Assets for Plan Benefits, Noncurrent	11.8	0
Defined Benefit Pension Plan Liabilities, Current	(1.3)	(1.2)
Defined Benefit Pension Plan, Liabilities, Noncurrent	(157.9)	(273.8)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assets for Plan Benefits, Noncurrent	0	0
Postemployment Benefits Liability, Current	(28.6)	(29.4)
Other Postretirement Defined Benefit Plan, Liabilities, Noncurrent	(572.7)	(559.0)
Other Postretirement Defined Benefit Plan, Liabilities	$ (601.3)	$ (588.4)