Consolidated Statements of Stockholder's Equity (Unaudited) (Parenthetical) - shares shares in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stockholders' Equity [Roll Forward]
Exercise of employee stock options (in shares)	0.0	0.1	0.2	0.2
Business acquisitions (in shares)				1.4

Number of share options (or share units) exercised during the current period.

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