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		148,036	217,560	237,650
Intrinsic value of settled performance units		$ 18.7	$ 9.7	$ 6.7
Tax benefit from distribution of performance units		$ 4.4	$ 2.2	$ 2.1
Performance units outstanding		539,475
Liability recorded on balance sheet		$ 58.1
Compensation cost not yet recognized		$ 20.5
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	140,455
Intrinsic value of settled performance units	$ 34.2
Tax benefit from distribution of performance units	$ 8.4