Stock-Based Compensation - Options outstanding (Details) - Stock options shares in Thousands	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Options Outstanding
Number Outstanding (in shares) | shares	48,751
Weighted Average Remaining Contractual Life	4 years 4 months 6 days
Weighted Average Exercise Price (in dollars per share)	$ 55.25
Options Exercisable
Number Exercisable (in shares) | shares	48,751
Weighted Average Exercise Price (in dollars per share)	$ 55.25
$29.05–$37.41
Information about options outstanding
Low end of exercise price range (in dollars per share)	29.05
High end of exercise price range (in dollars per share)	$ 54.76
Options Outstanding
Number Outstanding (in shares) | shares	17,933
Weighted Average Remaining Contractual Life	3 years 5 months 19 days
Weighted Average Exercise Price (in dollars per share)	$ 50.64
Options Exercisable
Number Exercisable (in shares) | shares	17,933
Weighted Average Exercise Price (in dollars per share)	$ 50.64
$54.76–$54.76
Information about options outstanding
Low end of exercise price range (in dollars per share)	57.47
High end of exercise price range (in dollars per share)	$ 57.47
Options Outstanding
Number Outstanding (in shares) | shares	22,372
Weighted Average Remaining Contractual Life	4 years 9 months 22 days
Weighted Average Exercise Price (in dollars per share)	$ 57.47
Options Exercisable
Number Exercisable (in shares) | shares	22,372
Weighted Average Exercise Price (in dollars per share)	$ 57.47
$57.47–$60.10
Information about options outstanding
Low end of exercise price range (in dollars per share)	57.95
High end of exercise price range (in dollars per share)	$ 60.10
Options Outstanding
Number Outstanding (in shares) | shares	8,446
Weighted Average Remaining Contractual Life	5 years 4 days
Weighted Average Exercise Price (in dollars per share)	$ 59.17
Options Exercisable
Number Exercisable (in shares) | shares	8,446
Weighted Average Exercise Price (in dollars per share)	$ 59.17