Stock Plans and Share-Based Compensation - Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Outstanding, weighted-average remaining contractual life (in years)	7 years 8 months 12 days
Exercisable, weighted-average remaining contractual life (in years)	6 years 10 months 24 days
Outstanding, aggregate intrinsic value | $	$ 139
Exercisable, aggregate intrinsic value | $	$ 50
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Outstanding beginning of period (in shares) | shares	4,163
Granted (in shares) | shares	1,009
Forfeited (in shares) | shares	(169)
Exercised (in shares) | shares	(330)
Outstanding end of period (in shares) | shares	4,673
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 29.52
Granted (in dollars per share) | $ / shares	54.19
Forfeited (in dollars per share) | $ / shares	37.18
Exercised (in dollars per share) | $ / shares	24.99
Outstanding at end of period (in dollars per share) | $ / shares	$ 34.89
Exercisable (in shares) | shares	1,268
Exercisable (in dollars per share) | $ / shares	$ 24.99