Employee Benefit Plans - Change in Benefit Obligation and Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	$ 625.8
Fair value of plan assets at end of year	636.6	$ 625.8
Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	734.5	824.0
Service cost	1.5	2.6	$ 3.6
Interest cost	28.0	27.3	28.9
Plan amendments	0.0	4.3
Actuarial loss (gain)	71.5	(63.2)
Change in GM portion of OPEB obligation	0.0	0.0
Participant contributions	0.2	0.3
Curtailments	(1.9)	(11.6)
Settlements	(28.8)	(0.6)
Benefit payments	(44.1)	(39.7)
Sale of business	(26.2)	0.0
Currency fluctuations	5.5	(9.4)
Other	0.0	0.5
Net change	5.7	(89.5)
Benefit obligation at end of year	740.2	734.5	824.0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	625.8	702.2
Actual return on plan assets	87.5	(31.0)
Employer contributions	10.0	4.4
Participant contributions	0.2	0.3
Benefit payments	(44.1)	(39.8)
Settlements	(28.8)	(0.6)
Sale of business	(20.7)	0.0
Currency fluctuations	6.7	(9.7)
Net change	10.8	(76.4)
Fair value of plan assets at end of year	636.6	625.8	702.2
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	537.3	613.3
Service cost	0.3	0.4	0.3
Interest cost	12.8	12.4	13.3
Plan amendments	0.0	(2.3)
Actuarial loss (gain)	11.9	(43.8)
Change in GM portion of OPEB obligation	3.1	(32.6)
Participant contributions	0.0	0.0
Curtailments	0.0	(0.2)
Settlements	0.0	0.0
Benefit payments	(15.5)	(9.9)
Sale of business	(0.8)	0.0
Currency fluctuations	0.0	0.0
Other	0.0	0.0
Net change	11.8	(76.0)
Benefit obligation at end of year	549.1	537.3	613.3
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	15.5	9.9
Participant contributions	0.0	0.0
Benefit payments	(15.5)	(9.9)
Settlements	0.0	0.0
Sale of business	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