Guarantees (Details) $ in Millions	Dec. 31, 2019 USD ($)
Guarantor Obligations
Total guarantees	$ 156.0
Guarantees expiring in less than one year	22.2
Guarantees expiring within one to three years	0.4
Guarantees with expiration over three years	133.4
Guarantees supporting transactions of subsidiaries
Guarantor Obligations
Total guarantees	31.4
Guarantees expiring in less than one year	10.2
Guarantees expiring within one to three years	0.2
Guarantees with expiration over three years	21.0
Guarantees supporting transactions of subsidiaries | UMERC
Guarantor Obligations
Total guarantees	4.0
Guarantees supporting transactions of subsidiaries | Bluewater
Guarantor Obligations
Total guarantees	6.2
Guarantees supporting transactions of subsidiaries | WECI
Guarantor Obligations
Total guarantees	21.2
Standby letters of credit
Guarantor Obligations
Total guarantees	103.0
Guarantees expiring in less than one year	1.2
Guarantees expiring within one to three years	0.2
Guarantees with expiration over three years	101.6
Surety bonds
Guarantor Obligations
Total guarantees	9.9
Guarantees expiring in less than one year	9.9
Guarantees expiring within one to three years	0.0
Guarantees with expiration over three years	0.0
Other guarantees
Guarantor Obligations
Total guarantees	11.7
Guarantees expiring in less than one year	0.9
Guarantees expiring within one to three years	0.0
Guarantees with expiration over three years	10.8
Other indemnification
Guarantor Obligations
Total guarantees	11.7
Liability related to workers compensation coverage	$ 10.8