Equity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	May. 31, 2014
Stock option activity
Options outstanding at the beginning of the period (in shares)	27,787,920	26,844,452	26,893,438
Options granted (in shares)	6,490,200	6,220,000	5,576,000
Options exercised (in shares)	(2,718,745)	(4,790,252)	(5,272,426)
Options forfeited (in shares)	(422,900)	(486,280)	(352,560)
Options outstanding at the end of the period (in shares)	31,136,475	27,787,920	26,844,452	26,893,438
Vested and non-vested options expected to vest at the end of the period (in shares)	28,749,963
Exercisable at the end of the period (in shares)	13,813,435
Weighted Average Exercise Price
Weighted average exercise price, options outstanding at the beginning of the period (in dollars per share)	$ 31.60	$ 25.90	$ 21.70
Weighted average exercise price, options granted (in dollars per share)	57.85	47.70	39.00
Weighted average exercise price, options exercised (in dollars per share)	23.71	20.27	18.23
Weighted average exercise price, options forfeited (in dollars per share)	41.73	34.55	26.83
Weighted average exercise price, options outstanding at the end of the period (in dollars per share)	37.62	$ 31.60	$ 25.90	$ 21.70
Weighted average exercise price, vested and non-vested options expected to vest (in dollars per share)	37.04
Weighted average exercise price, exercisable (in dollars per share)	$ 26.84
Stock Options
Weighted Average Remaining Contractual Term
Weighted average remaining contractual term of options outstanding	6 years 11 months 1 day	7 years 1 month 2 days	7 years 29 days	7 years 29 days
Weighted average remaining contractual term of options vested options and non-vested expected to vest	6 years 9 months 26 days
Weighted average remaining contractual term of options exercisable	5 years 3 months 29 days
Aggregate Intrinsic Value
Aggregate intrinsic value of options outstanding	$ 491.0
Aggregate intrinsic value of options, vested and non-vested options expected to vest	468.4
Aggregate intrinsic value of options exercisable	$ 350.7
Status of the Company's non-vested options and changes during the year
Non-vested options at the beginning of the period (in shares)	16,440,560
Non-vested options, options granted (in shares)	6,490,200
Non-vested options, options vested (in shares)	(5,184,820)
Non-vested options, options forfeited (in shares)	(422,900)
Non-vested options at the end of the period (in shares)	17,323,040	16,440,560
Weighted Average Fair Value at Grant Date
Weighted average fair value at the grant date, options outstanding at the beginning of the period (in dollars per share)	$ 7.98
Weighted average fair value at grant date, options granted (in dollars per share)	8.47	$ 8.64	$ 8.71
Weighted average fair value at grant date, options vested (in dollars per share)	7.70
Weighted average fair value at grant date, options forfeited (in dollars per share)	8.18
Weighted average fair value at the grant date, options outstanding at the end of the period (in dollars per share)	$ 8.24	$ 7.98
Total intrinsic value of stock options exercised	$ 88.1	$ 136.8	$ 105.8
Total fair value of stock options vested	39.9	37.2	33.9
Total compensation cost related to non-vested options not yet recognized	$ 104.9
Weighted average expected amortization period	3 years 4 months 10 days
Restricted Stock
Weighted Average Fair Value at Grant Date
Total fair value of restricted share awards vested	$ 0.9	$ 1.0	$ 0.9
Total compensation cost related to non-vested options not yet recognized	$ 0.4
2000 Employee Option Plan
Stock-Based Compensation:
Number of additional stock options that can be granted (in shares)	0
2009 Employee Option Plan
Stock-Based Compensation:
Common Stock reserved for issuance					58,000,000
Shares available for the granting of additional stock options	18,911,280
Options ratable vesting period	5 years
2000 Employee Option Plan and 2009 Employee Option Plan
Stock-Based Compensation:
Options exercisable period	10 years
2004 Directors Option Plan
Stock-Based Compensation:
Shares available for the granting of additional stock options	140,000
Options exercisable period	10 years
Number of additional stock options expected to be granted (in shares)	0
2012 Directors Restricted Stock Plan | Restricted Stock
Stock-Based Compensation:
Shares available for the granting of additional stock options	153,974
Stock option activity
Shares vested and issued (in shares)	(19,032)	(26,880)	(32,858)
Weighted Average Fair Value at Grant Date
Fair value of restricted shares vested and issued (in dollar per share)	$ 47.98	$ 38.76	$ 26.63
Restricted share activity
Restricted shares outstanding at the beginning of the period (in shares)	18,340	26,880	32,858
Restricted shares granted	17,948	18,340	26,880
Shares vested and issued (in shares)	(19,032)	(26,880)	(32,858)
Restricted shares outstanding at the end of the period (in shares)	17,256	18,340	26,880	32,858
Fair Value at Grant Date
Fair value at the grant date, restricted shares outstanding at the beginning of the period (in dollars per share)	$ 47.72	$ 38.76	$ 26.63
Fair value of restricted shares granted (in dollars per share)	57.85	47.72	38.76
Fair value of restricted shares vested and issued (in dollar per share)	47.98	38.76	26.63
Fair value at the grant date, restricted shares outstanding at the end of the period (in dollars per share)	$ 57.97	$ 47.72	$ 38.76	$ 26.63
Weighted Average Remaining Amortization Term (in years)	4 months 21 days	4 months 21 days	4 months 21 days