Segment Information (Identifiable Assets by Business Segment) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Identifiable assets	$ 15,403.6	$ 15,469.6
Discontinued operations	102.6	88.0
U.S. Companies [Member]
Segment Reporting Information [Line Items]
Identifiable assets	11,049.8	10,909.2
Chaucer [Member]
Segment Reporting Information [Line Items]
Identifiable assets	$ 4,251.2	$ 4,472.4

Amount classified as assets attributable to disposal group held for sale or disposed of.

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