Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net Income	$ 70.5	$ 51.0
Other Comprehensive Income (Loss) [Abstract]
Unrealized Gain (Loss) on Securities Net of Income Tax Expense of $– and $–	0.1	(0.1)
Defined Benefit Pension and Other Postretirement Benefit Plans Net of Income Tax Expense of $0.1 and $0.1	0.0	0.4
Total Other Comprehensive Income	0.1	0.3
Total Comprehensive Income	$ 70.6	$ 51.3

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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