Earnings Per Share (Tables)

12 Months Ended

Dec. 31, 2018

Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]

Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]

The following table sets forth the computation of basic and diluted earnings per share:

	Year ended December 31,
Share amounts in millions	2018	2017	2016
Denominator for basic earnings per share:
Weighted average common shares outstanding	143.0	144.4	143.4
Effect of dilutive securities:
Dilutive effect of employee stock plans	1.4	2.0	1.7
Dilutive effect of stock warrants	—	—	0.2
Dilutive potential common shares	1.4	2.0	1.9
Denominator for diluted earnings per share:
Adjusted weighted average shares	144.4	146.4	145.3