Share Tracking Awards Plans - General (Details) - Share tracking award plans (STAP) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Awards granted under the STAP
Grant expiration period from the grant date	10 years
Share-based awards, vesting period	4 years
Aggregate STAP liability	$ 184.7		$ 354.7
Long term portion of STAP liability	$ 50.0		$ 80.2
Assumptions used to measure the fair value of STAP awards
Expected volatility (as a percent)	35.50%	34.50%
Risk-free interest rate (as a percent)	0.90%	1.20%
Expected term of awards	2 years 9 months 18 days	4 years 1 month 6 days
Expected forfeiture rate (as a percent)	10.20%	9.60%
Expected dividend yield (as a percent)	0.00%	0.00%
Closing price of common stock (in dollars per share)	$ 118.08	$ 131.24
Share-based awards activity
Outstanding at the beginning of the year (in shares)	6,845,163
Exercised (in shares)	(914,642)
Forfeited (in shares)	(544,507)
Outstanding at the end of the period (in shares)	5,386,014
Exercisable at the end of the period (in shares)	2,797,117
Expected to vest at the end of the period (in shares)	2,316,622
Share awards, Weighted-Average Exercise Price
Outstanding at the beginning of the year (in dollars per share)	$ 86.86
Exercised (in dollars per share)	61.41
Forfeited (in dollars per share)	94.00
Outstanding at the end of the period (in dollars per share)	90.46
Exercisable at the end of the period (in dollars per share)	86.50
Expected to vest at the end of the period (in dollars per share)	$ 94.33
Share awards, Weighted Average Remaining Contractual Term
Outstanding at the end the period	6 years 8 months 12 days
Exercisable at the end of the period	6 years 2 months 12 days
Expected to vest at the end of the period	7 years 2 months 12 days
Share awards, Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	$ 208.2
Exercisable at the end of the period (in dollars)	113.5
Expected to vest at the end of the period (in dollars)	$ 85.4
Awards granted during the period, weighted average grant date fair value (in dollars per share)		$ 58.52