Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of tax benefit from the vesting or payment of awards under share-based compensation arrangements.

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Common Equity - Performance Units (Details) - Performance units - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance units granted		22,452	32,650	34,765
Intrinsic value of settled performance units		$ 2.3	$ 2.0	$ 1.4
Tax benefit from distribution of performance units		$ 0.5	$ 0.4	$ 0.4
Performance units outstanding		66,051
Liability recorded on balance sheet		$ 6.6
Compensation cost not yet recognized		$ 9.8
Weighted-average period over which unrecognized compensation cost is expected to be recognized		1 year 7 months 6 days
Subsequent event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance units granted	18,952
Intrinsic value of settled performance units	$ 3.7
Tax benefit from distribution of performance units	$ 0.9