Share-based compensation (Tables)

3 Months Ended

Mar. 31, 2020

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Unrecognized Compensation Cost Associated with Unvested Awards and Weighted Average Period Over Which it is Expected to be Recognized

The following tables present unrecognized compensation cost associated with unvested awards and weighted average period over which it is expected to be recognized:

(Millions)	March 31, 2020
	PSUs - IPO Incentive Awards		PSUs - 2019 Long Term Incentive (LTI)		RSUs		Stock Options		2018 Long Term Incentive Plan (LTIP)
Unrecognized compensation cost related to unvested awards	$	2.6	$	1.1	$	9.8	$	1.8	$	0.2
Weighted average recognition period (years)	1.8 years		1.8 years		1.7 years		1.9 years		0.8 years

Summary of Outstanding Share-settled Awards

The following table summarizes outstanding share-settled awards as of March 31, 2020:

As of and for the quarter ended March 31, 2020	Number of Shares
	PSUs - IPO Incentive Awards	PSUs - 2019 LTI	RSUs	Stock Options	2018 Long Term Incentive Plan (LTIP)
Unvested, beginning of period	555,163	391,136	1,353,852	1,374,945	870,471
Granted	—	—	—	—	—
Vested	—	—	—	—	—
Forfeited	11,967	8,809	33,015	—	14,372
Unvested, end of period	543,196	382,327	1,320,837	1,374,945	856,099