Summary of Significant Accounting Policies (Schedule of Prior Year Amounts Recast Affected by Cumulative Adjustment in Statements of Earnings and Comprehensive Income) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Loss on disposal of discontinued businesses, net of tax (benefit) of ($4.1)	$ (26.0)	$ (13.3)	$ (105.2)
Net loss from operations	(27.8)	(3.7)	(101.0)
Net earnings	214.5	185.9	119.6
Total comprehensive income	$ 297.9	$ 126.5	$ 177.5
(Loss) per share of common stock, discontinued operations:
Basic	$ (0.57)	$ (0.07)	$ (1.89)
Diluted	(0.56)	(0.07)	(1.87)
Net earnings per share of common stock:
Basic	4.40	3.61	2.23
Diluted	$ 4.32	$ 3.56	$ 2.21
As Reported [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Loss on disposal of discontinued businesses, net of tax (benefit) of ($4.1)			$ (70.0)
Net loss from operations			(65.8)
Net earnings			154.8
Total comprehensive income			$ 212.7
(Loss) per share of common stock, discontinued operations:
Basic			$ (1.23)
Diluted			(1.22)
Net earnings per share of common stock:
Basic			2.89
Diluted			$ 2.86