Earnings Per Share (Details) - shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive shares (in shares)	5.5	6.8	5.4	6.5
Share Options and Appreciation Rights [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive shares (in shares)	1.5	1.9	1.5	1.9
Novested Restricted Shares and Restricted Share Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive shares (in shares)	4.0	4.9	3.9	4.6