Stock-Based Compensation, Stock Option and Restricted Shares (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
2000 Employee Option Plan
Stock-Based Compensation
Options exercisable period	10 years
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
Shares available for the granting of additional stock options	23,016,700
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)	33,222,364
Options exercised (in shares)	(602,549)
Options forfeited (in shares)	(32,240)
Options outstanding at the end of the period (in shares)	32,587,575		33,222,364
Vested and non-vested options expected to vest at the end of the period (in shares)	30,726,902
Exercisable at the end of the period (in shares)	13,086,775
Weighted Average Exercise Price
Weighted average exercise price, options outstanding at the beginning of the period (in dollars per share)	$ 52.27
Weighted average exercise price, options outstanding at the end of the period (in dollars per share)	52.58		$ 52.27
Weighted average exercise price, vested and non-vested options expected to vest (in dollars per share)	51.92
Weighted average exercise price, exercisable (in dollars per share)	$ 39.76
Weighted Average Remaining Contractual Term
Weighted average remaining contractual term of options outstanding	6 years 10 months 2 days		7 years 18 days
Weighted average remaining contractual term of options vested options and non-vested expected to vest	6 years 9 months 4 days
Weighted average remaining contractual term of options exercisable	5 years 2 months 12 days
Aggregate Intrinsic Value
Aggregate intrinsic value of options outstanding	$ 1,093.2		$ 1,180.3
Aggregate intrinsic value of options, vested and non-vested options expected to vest	1,051.0
Aggregate intrinsic value of options exercisable	$ 606.8
Status of the Company's non-vested options and changes during the year
Non-vested options at the beginning of the period (in shares)	19,600,440
Non-vested options, options vested (in shares)	(67,400)
Non-vested options, options forfeited (in shares)	(32,240)
Non-vested options at the end of the period (in shares)	19,500,800		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)	$ 8.29
Weighted average fair value at grant date, options vested (in dollars per share)	8.13
Weighted average fair value at grant date, options forfeited (in dollars per share)	8.56
Weighted average fair value at the grant date, options outstanding at the end of the period (in dollars per share)	$ 8.29		$ 8.29
Fair Value at Grant Date
Total intrinsic value of stock options exercised (in dollars)	$ 34.3	$ 34.5
Total fair value of stock options vested (in dollars)	0.5	$ 0.7
Total compensation cost related to non-vested options not yet recognized (in dollars)	$ 108.5
Weighted average expected amortization period	3 years 1 month 21 days
Restricted Shares | 2012 Directors Restricted Stock Plan
Stock-Based Compensation
Shares available for the granting of additional stock options	124,164
Restricted share activity
Restricted shares outstanding at the beginning of the period (in shares)	12,905
Restricted shares outstanding at the end of the period (in shares)	12,905		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)	$ 73.25
Fair value at the grant date, restricted shares outstanding at the end of the period (in dollars per share)	$ 73.25		$ 73.25
Weighted Average Remaining Amortization Term (in years)	1 month 17 days		4 months 13 days
Total compensation cost related to non-vested restricted shares not yet recognized (in dollars)	$ 0.1
Weighted average expected amortization period	1 month 17 days