Significant Accounting Policies - Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Schedule of ant-dilutive securities excluded from computation of diluted earnings (loss) per share

The shares that were not included in the computation of diluted earnings per share for those periods because their inclusion would be anti-dilutive were as follows:

(millions, common shares)	2017	2016	2015
Stock options, RSUs, MSUs and performance shares	0.7	1.5	1.9
Deferred shares associated with a deferred compensation program for non-employee directors	0.2	0.2	—