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Stock-based compensation (Summary of Stock Options) (Details) - Stock options [Member]
$ / shares in Units, shares in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2019
USD ($)
$ / shares
shares
Options  
Balance unexercised at beginning of period (in shares) | shares 4.4
Granted (in shares) | shares 1.4
Exercised (in shares) | shares (0.7)
Expired/forfeited (in shares) | shares (0.3)
Balance unexercised at end of period (in shares) | shares 4.8
Vested or expected to vest (in shares) | shares 4.6
Exercisable (in shares) | shares 1.3
Weighted- average exercise price  
Balance unexercised at beginning of period (in usd per share) | $ / shares $ 143.57
Granted (in usd per share) | $ / shares 177.31
Exercised (in usd per share) | $ / shares 107.13
Expired/forfeited (in usd per share) | $ / shares 171.01
Balance unexercised at end of period (in shares) | $ / shares 157.00
Weighted-average exercise price, vested or expected to vest (in usd per share) | $ / shares 156.02
Weighted-average exercise price, exercisable (in usd per share) | $ / shares $ 117.13
Stock options information [Abstract]  
Weighted-average remaining contractual life (years), unexercised 7 years 2 months 12 days
Weighted-average remaining contractual life (years), vested or expected to vest 7 years 1 month 6 days
Weighted-average remaining contractual life (years), exercisable 4 years 3 months 18 days
Aggregate intrinsic value, unexercised | $ $ 406
Aggregate intrinsic value, vested or expected to vest | $ 390
Aggregate intrinsic value, exercisable | $ $ 162