Stock-Based Compensation, Stock Option and Restricted Shares (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				6 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
2009 Employee Option Plan
Stock-Based Compensation
Number of additional stock options that will be granted (in shares)						0
Options ratable vesting period						5 years
Options exercisable period						10 years
2017 Employee Option Plan
Stock-Based Compensation
Common Stock reserved for issuance	30,000,000					30,000,000
Shares available for the granting of additional stock options	17,002,620					17,002,620
Options ratable vesting period						5 years
Options exercisable period						10 years
2004 Directors Option Plan
Stock-Based Compensation
Options exercisable period						10 years
Stock Options
Stock option activity
Options outstanding at the beginning of the period (in shares)	37,841,889	32,587,575	33,222,364		33,222,364	33,222,364
Options granted (in shares)	91,000	6,111,100
Options exercised (in shares)	(1,952,700)	(740,046)	(602,549)
Options forfeited (in shares)	(226,020)	(116,740)	(32,240)
Options outstanding at the end of the period (in shares)	35,754,169	37,841,889	32,587,575		37,841,889	35,754,169		33,222,364
Vested and non-vested options expected to vest at the end of the period (in shares)	33,489,508					33,489,508
Exercisable at the end of the period (in shares)	16,426,149					16,426,149
Weighted Average Exercise Price
Weighted average exercise price, options outstanding at the beginning of the period (in dollars per share)	$ 58.50	$ 52.58	$ 52.27		$ 52.27	$ 52.27
Weighted average exercise price, options outstanding at the end of the period (in dollars per share)	59.68	$ 58.50	$ 52.58		$ 58.50	59.68		$ 52.27
Weighted average exercise price, vested and non-vested options expected to vest (in dollars per share)	58.93					58.93
Weighted average exercise price, exercisable (in dollars per share)	$ 46.22					$ 46.22
Weighted Average Remaining Contractual Term
Weighted average remaining contractual term of options outstanding			6 years 10 months 2 days		7 years 1 month 24 days	7 years 18 days		7 years 18 days
Weighted average remaining contractual term of options vested options and non-vested expected to vest						6 years 11 months 19 days
Weighted average remaining contractual term of options exercisable						5 years 6 months 18 days
Aggregate Intrinsic Value
Aggregate intrinsic value of options outstanding	$ 1,227.9	$ 1,089.4	$ 1,093.2		$ 1,089.4	$ 1,227.9		$ 1,180.3
Aggregate intrinsic value of options, vested and non-vested options expected to vest	1,175.0					1,175.0
Aggregate intrinsic value of options exercisable	$ 785.2					$ 785.2
Status of the Company's non-vested options and changes during the year
Non-vested options at the beginning of the period (in shares)	19,571,980	19,500,800	19,600,440		19,600,440	19,600,440
Options granted (in shares)	91,000	6,111,100
Non-vested options, options vested (in shares)	(108,940)	(5,923,180)	(67,400)
Non-vested options, options forfeited (in shares)	(226,020)	(116,740)	(32,240)
Non-vested options at the end of the period (in shares)	19,328,020	19,571,980	19,500,800		19,571,980	19,328,020		19,600,440
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)	$ 9.69	$ 8.29	$ 8.29		$ 8.29	$ 8.29
Weighted average fair value at grant date, options granted (in dollars per share)	12.82	12.82
Weighted average fair value at grant date, options vested (in dollars per share)	8.40	8.35	8.13
Weighted average fair value at grant date, options forfeited (in dollars per share)	9.48	8.18	8.56
Weighted average fair value at the grant date, options outstanding at the end of the period (in dollars per share)	$ 9.71	$ 9.69	$ 8.29		$ 9.69	$ 9.71		$ 8.29
Fair Value at Grant Date
Total intrinsic value of stock options exercised (in dollars)	$ 111.8			$ 77.0		$ 181.1	$ 191.1
Total fair value of stock options vested (in dollars)	0.9			$ 0.7		50.9	$ 46.2
Total compensation cost related to non-vested options not yet recognized (in dollars)	$ 152.8					$ 152.8
Weighted average expected amortization period						3 years 6 months 26 days
Restricted Shares | 2012 Directors Restricted Stock Plan
Stock-Based Compensation
Shares available for the granting of additional stock options	109,695					109,695
Restricted share activity
Restricted shares outstanding at the beginning of the period (in shares)	14,328	12,905	12,905		12,905	12,905
Restricted shares granted (in shares)		14,469
Shares vested and issued (in shares)		(13,046)
Restricted shares outstanding at the end of the period (in shares)	14,328	14,328	12,905		14,328	14,328		12,905
Fair Value at Grant Date
Fair value at the grant date, restricted shares outstanding at the beginning of the period (in dollars per share)	$ 87.98	$ 73.25	$ 73.25		$ 73.25	$ 73.25
Fair value of restricted shares vested and issued (in dollar per share)		73.35
Fair value of restricted shares granted (in dollars per share)		87.93
Fair value at the grant date, restricted shares outstanding at the end of the period (in dollars per share)	$ 87.98	$ 87.98	$ 73.25		$ 87.98	$ 87.98		$ 73.25
Weighted Average Remaining Amortization Term (in years)			1 month 17 days		10 months 17 days	7 months 17 days		4 months 13 days
Total compensation cost related to non-vested restricted shares not yet recognized (in dollars)	$ 0.8					$ 0.8
Weighted average expected amortization period						7 months 17 days