Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Options, Outstanding, Shares
Options, Beginning balance (shares)	0.7
Shares, exercised (shares)	(0.2)
Shares, forfeited and expired (shares)	0.0	(0.1)
Options, Ending balance (shares)	0.5	0.7
Shares, options exercisable (shares)	0.5
Weighted average exercise price
Weighted-average exercise price, Beginning balance (USD per share)	$ 55.73
Weighted-average exercise price, exercised (USD per share)	280.79
Weighted-average exercise price, forfeited and expired (USD per share)	58.06
Weighted-average exercise price, Ending balance (USD per share)	60.46	$ 55.73
Weighted-average exercise price, options exercisable (USD per share)	$ 60.34
Aggregate intrinsic value, options outstanding	$ 123.0
Aggregate intrinsic value, options exercisable	$ 122.0
Non Vested Options
Weighted average exercise price
Weighted-average remaining years of contractual term, Options outstanding	2 years 6 months 21 days
Weighted-average remaining years of contractual term, Options exercisable	2 years 6 months 10 days
Nonvested Options Outstanding
Options, Beginning balance (shares)	0.0
Shares, vested (less than) (shares)	(0.1)
Shares, forfeited (shares)	0.0
Options, Ending balance (less than) (shares)	0.1	0.0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Total unrecognized compensation expense related to nonvested options	$ 0.0
Weighted-average years to be recognized over	2 months 12 days
Weighted-average grant-date fair value
Weighted-average grant-date fair value, Beginning balance (USD per share)	$ 112.68
Weighted-average grant-date fair value, vested (USD per share)	113.14
Weighted-average exercise price, forfeited (USD per share)	113.40
Weighted-average grant-date fair value, Beginning balance (USD per share)	$ 111.96	$ 112.68