Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net Income	$ 155.3	$ 53.8
Other Comprehensive Income (Loss) Before Income Taxes:
Unrealized Holding Gains (Losses)	162.8	(121.4)
Foreign Currency Translation Adjustments	0.0	(0.9)
Decrease in Net Unrecognized Postretirement Benefit Costs	0.6	0.3
Gain on Cash Flow Hedges	0.1	0.9
Other Comprehensive Income (Loss) Before Income Taxes	163.5	(121.1)
Other Comprehensive Income Tax Benefit (Expense)	(34.4)	25.4
Other Comprehensive Income (Loss)	129.1	(95.7)
Total Comprehensive Income (Loss)	$ 284.4	$ (41.9)

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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