Shares Used in Computing Net Income Per Share - Schedule of Weighted-Average Number of Shares (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Weighted-average common shares outstanding used for the calculation of net income per share – basic	403.8	420.2	408.4	424.3
Common stock equivalents (in shares)	8.2	8.9	8.2	9.1
Weighted-average common shares outstanding used for the calculation of net income per share – diluted	412.0	429.1	416.6	433.4