Consolidated Statements of Stockholder's Equity (Parenthetical) - shares shares in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Stockholders' Equity [Roll Forward]
Exercise of employee stock options (in shares)	0.5	1.2
Acquisitions (in shares)	1.5	0.2

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

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Balance Type:	na
Period Type:	duration