Earnings per Share - Antidilutive Securities Excluded From EPS Calculation (Details) - shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive effect excluded from the computation of diluted weighted-average shares outstanding (in shares)	4.4	3.9	4.4	3.8
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive effect excluded from the computation of diluted weighted-average shares outstanding (in shares)	3.3	3.2	3.3	3.1
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive effect excluded from the computation of diluted weighted-average shares outstanding (in shares)	0.1	0.3	0.2	0.4
Performance stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive effect excluded from the computation of diluted weighted-average shares outstanding (in shares)	1.0	0.4	0.9	0.3