Quarterly Results of Operations (Schedule of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended												12 Months Ended
	Dec. 30, 2018	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Total revenues		$ 1,102.8		$ 1,166.6		$ 1,133.4		$ 1,091.5		$ 1,092.5	$ 1,085.9	$ 1,053.3	$ 1,036.2	$ 4,494.3	$ 4,267.9	$ 4,053.9
Income from continuing operations		2.1		104.0		82.4		50.5		71.9	59.5	56.3	28.4	239.0	216.1	67.0
Net income		$ 123.6		$ 100.4		$ 99.3		$ 67.7		$ 51.5	$ 11.1	$ 78.4	$ 45.2	$ 391.0	$ 186.2	$ 155.1
Income from continuing operations per share, Basic		$ 0.05		$ 2.45		$ 1.94		$ 1.19		$ 1.69	$ 1.40	$ 1.32	$ 0.67	$ 5.63	$ 5.08	$ 1.57
Income from continuing operations per share, Diluted		0.05		2.41		1.91		1.17		1.67	1.38	1.32	0.66	5.56	5.03	1.55
Net income per share, Basic		2.92		2.36		2.34		1.59		1.21	0.26	1.84	1.06	9.21	4.38	3.63
Net income per share, Diluted		2.88		2.33		2.31		1.57		1.20	0.26	1.83	1.05	$ 9.09	$ 4.33	$ 3.59
Dividends declared per share	$ 4.75	$ 5.35	[1]	$ 0.54	[1]	$ 0.54	[1]	$ 0.54	[1]	$ 0.54	$ 0.50	$ 0.50	$ 0.50

[1] As a result of the sale of Chaucer, (see Note 2 – “Discontinued Operations”), on December 30, 2018 the Board of Directors declared a special dividend of $4.75 per share (see Note 12 – “Earnings Per Share and Shareholders’ Equity Transactions”).