Employee Benefit Plans Change in Benefit Obligation and Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Settlements		$ (131.1)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	$ 643.7
Fair value of plan assets at end of year	612.8	643.7
Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at end of year	738.8	755.4
Service cost	3.2	3.5	$ 3.4
Interest cost	28.6	36.1	33.8
Actuarial loss (gain)	(32.1)	119.3
Change in GM Portion of OPEB Obligation	0.0	0.0
Participant contributions	0.4	0.4
Settlements	0.0	(131.1)
Benefit payments	(38.4)	(36.5)
Currency fluctuations	(7.4)	(8.3)
Defined Benefit Plan, Benefit Obligation, Period Increase (Decrease)	(45.7)	(16.6)
Benefit obligation at end of year	693.1	738.8	755.4
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	643.7	713.4
Actual return on plan assets	(5.0)	77.2
Employer contributions	20.1	1.9
Participant contributions	0.4	0.4
Benefit payments	(38.4)	(36.5)
Defined Benefit Plan, Settlements, Plan Assets	0.0	(104.2)
Currency fluctuations	(8.0)	(8.5)
Net change	(30.9)	(69.7)
Fair value of plan assets at end of year	612.8	643.7	713.4
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at end of year	654.7	577.9
Service cost	0.4	0.3	0.4
Interest cost	15.0	15.3	13.2
Actuarial loss (gain)	(35.9)	41.2
Change in GM Portion of OPEB Obligation	(31.6)	31.8
Participant contributions	0.0	0.0
Settlements	0.0	0.0
Benefit payments	(14.2)	(11.8)
Currency fluctuations	0.0	0.0
Defined Benefit Plan, Benefit Obligation, Period Increase (Decrease)	(66.3)	76.8
Benefit obligation at end of year	588.4	654.7	577.9
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0.0	0.0
Actual return on plan assets	0.0	0.0
Employer contributions	14.2	11.8
Participant contributions	0.0	0.0
Benefit payments	(14.2)	(11.8)
Defined Benefit Plan, Settlements, Plan Assets	0.0	0.0
Currency fluctuations	0.0	0.0
Net change	0.0	0.0
Fair value of plan assets at end of year	$ 0.0	$ 0.0	$ 0.0
Change in Mortality Rate Assumptions [Member] | Pension Plan [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Explanation of Significant Change in Benefit Obligation or Plan Assets Not Apparent from Other Required Disclosures		25.2
Change in Mortality Rate Assumptions [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Explanation of Significant Change in Benefit Obligation or Plan Assets Not Apparent from Other Required Disclosures		19.0