Stock Compensation Plans (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock Compensation Plans:
Stock compensation expense	$ 315.0	$ 285.0	$ 261.0
Stock compensation expense recognized in merger costs		$ 5.0	$ 49.0
Roll Forward of Stock Options Outstanding:
Stock options outstanding, beginning of period (in shares)	10,410,000	9,649,000	9,592,000
Stock options granted (in shares)	1,847,000	1,507,000	1,175,000
Stock options exercised (in shares)	(1,271,000)	(577,000)	(1,044,000)
Stock options canceled (in shares)	(437,000)	(169,000)	(74,000)
Stock options outstanding, end of period (in shares)	10,549,000	10,410,000	9,649,000
Stock options outstanding weighted average exercise price, beginning of period	$ 225.53	$ 201.83	$ 181.39
Stock options granted weighted average exercise price	298.84	350.40	302.87
Stock options exercised weighted average exercise price	186.90	133.35	124.32
Stock options canceled weighted average exercise price	270.94	300.46	251.63
Stock options outstanding weighted average exercise price, end of period	$ 241.14	$ 225.53	$ 201.83
Stock options exercised aggregate intrinsic value	$ 247.0	$ 114.0	$ 219.0
Stock options outstanding aggregate intrinsic value	$ 2,573.0
Stock options outstanding weighted average remaining contractual life (in years)	7 years	7 years	8 years
Stock options exercisable, end of period (in shares)	3,119,000	2,194,000	1,734,000
Stock options exercisable weighted average exercise price, end of period	$ 161.13	$ 122.19	$ 90.56
Stock options exercisable aggregate intrinsic value, end of period	$ 1,011.0
Stock options expected to vest, end of period (in shares)	7,430,000
Stock options expected to vest weighted average exercise price, end of period	$ 274.74
Stock options expected to vest aggregate intrinsic value, end of period	$ 1,563.0
Stock options granted weighted average grant date fair value	$ 84.39	$ 94.70	$ 73.67
Stock Options
Stock Compensation Plans:
Award vesting period (in years)	3 years
Award expiration period (in years)	10 years
Unrecognized compensation expense	$ 175.0
Remaining period over which unrecognized compensation expense is expected to be recognized (in years)	2 years
Restricted Stock
Stock Compensation Plans:
Award vesting period (in years)	1 year
Unrecognized compensation expense	$ 0.9
Remaining period over which unrecognized compensation expense is expected to be recognized (in years)	4 months
Roll Forward of Restricted Stock and Restricted Stock Units Outstanding:
Awards other than stock options outstanding, beginning of period (in shares)	10,000	10,000	10,000
Awards other than stock options, granted (in shares)	8,000	10,000	10,000
Awards other than stock options, vested (in shares)	(10,000)	(10,000)	(10,000)
Awards other than stock options, canceled (in shares)	0	0	0
Awards other than stock options outstanding, end of period (in shares)	8,000	10,000	10,000
Awards other than stock options outstanding weighted average grant price, beginning of period	$ 297.86	$ 343.10	$ 231.81
Awards other than stock options granted weighted average grant price	359.33	297.86	343.10
Awards other than stock options vested weighted average grant price	297.86	343.10	231.81
Awards other than stock options canceled weighted average grant price	0	0	0
Awards other than stock options outstanding weighted average grant price, end of period	$ 359.33	$ 297.86	$ 343.10
Restricted Stock Units (RSUs)
Stock Compensation Plans:
Award vesting period (in years)	3 years
Unrecognized compensation expense	$ 205.0
Remaining period over which unrecognized compensation expense is expected to be recognized (in years)	2 years
Roll Forward of Restricted Stock and Restricted Stock Units Outstanding:
Awards other than stock options outstanding, beginning of period (in shares)	2,211,000	2,391,000	3,313,000
Awards other than stock options, granted (in shares)	704,000	526,000	285,000
Awards other than stock options, vested (in shares)	(729,000)	(619,000)	(1,159,000)
Awards other than stock options, canceled (in shares)	(127,000)	(87,000)	(48,000)
Awards other than stock options outstanding, end of period (in shares)	2,059,000	2,211,000	2,391,000
Awards other than stock options outstanding weighted average grant price, beginning of period	$ 219.61	$ 192.96	$ 192.41
Awards other than stock options granted weighted average grant price	298.22	348.75	302.76
Awards other than stock options vested weighted average grant price	206.88	216.27	216.21
Awards other than stock options canceled weighted average grant price	250.85	286.41	234.99
Awards other than stock options outstanding weighted average grant price, end of period	$ 249.45	$ 219.61	$ 192.96
Restricted Stock Units (RSUs) | Legacy TWC Awards Converted May 2016
Stock Compensation Plans:
Award vesting (percentage)	50.00%
Class A Common Stock
Stock Compensation Plans:
Shares authorized under the the stock incentive plan (in shares)	16,000,000
Roll Forward of Stock Options Outstanding:
Stock options exercised (in shares)	(1,271,419)	(576,583)	(1,044,526)
Roll Forward of Restricted Stock and Restricted Stock Units Outstanding:
Awards other than stock options, vested (in shares)	(728,553)	(618,649)	(1,159,083)