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Share-Based Payments - Narrative (Details) $ / shares in Units, shares in Millions, $ in Millions | 1 Months Ended | 12 Months Ended |
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Jun. 30, 2015 shares | Dec. 31, 2020 USD ($) Increment Plan $ / shares shares | Dec. 31, 2019 USD ($) $ / shares | Dec. 31, 2018 USD ($) $ / shares | Dec. 31, 2013 Increment | Jun. 30, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Unrecognized compensation cost related to unvested share-based compensation |  |  | $ 207.6 |  |  |  |  |
Weighted-average period to recognize the cost of unvested awards |  |  | 1 year 10 months 24 days |  |  |  |  |
Number of share-based compensation plans pursuant to which awards are currently being made | Plan |  |  | 3 |  |  |  |  |
Total intrinsic value of options exercised |  |  | $ 2.9 |  | $ 4.2 | $ 4.0 |  |
Shares issued under the 2015 ESPP (in shares) | shares |  | 6.2 |  |  |  |  |  |
Market stock units |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Number of equal annual increments | Increment |  |  | 3 |  |  |  | 4 |
Percentage of earnings of the target number of units granted based on actual stock performance |  |  | 0.00% |  |  |  | 0.00% |
Percentage of earnings of the target number of units granted based on actual stock performance |  |  | 200.00% |  |  |  | 150.00% |
Number of days for calculation of average closing stock price |  |  | 30 days |  |  |  |  |
Total fair value of vested awards |  |  | $ 26.9 |  | $ 32.5 | $ 26.9 |  |
Granted (in dollars per share) | $ / shares |  |  | $ 398.61 | [1] | $ 378.08 | $ 378.85 |  |
Cash settled performance units |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Number of equal annual increments | Increment |  |  | 3 |  |  |  |  |
Percentage of earnings of the target number of units granted based on actual stock performance |  |  | 0.00% |  |  |  |  |
Percentage of earnings of the target number of units granted based on actual stock performance |  |  | 200.00% |  |  |  |  |
Number of days for calculation of average closing stock price |  |  | 30 days |  |  |  |  |
Cash settlement of awards upon vesting |  |  | $ 3.8 |  | $ 10.6 | $ 15.1 |  |
Performance units |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Number of equal annual increments | Increment |  |  | 3 |  |  |  |  |
Percentage of earnings of the target number of units granted based on actual stock performance |  |  | 0.00% |  |  |  |  |
Percentage of earnings of the target number of units granted based on actual stock performance |  |  | 200.00% |  |  |  |  |
Number of days for calculation of average closing stock price |  |  | 30 days |  |  |  |  |
Cash settlement of awards upon vesting |  |  | $ 3.4 |  | 10.4 | 17.0 |  |
Performance stock units settled in stock |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Vesting period |  |  | 3 years |  |  |  |  |
Percentage of earnings of the target number of units granted based on actual stock performance |  |  | 0.00% |  |  |  |  |
Percentage of earnings of the target number of units granted based on actual stock performance |  |  | 200.00% |  |  |  |  |
Granted (in dollars per share) | $ / shares | [2] |  | $ 293.35 |  |  |  |  |
Performance stock units settled in cash |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Vesting period |  |  | 3 years |  |  |  |  |
Percentage of earnings of the target number of units granted based on actual stock performance |  |  | 0.00% |  |  |  |  |
Percentage of earnings of the target number of units granted based on actual stock performance |  |  | 200.00% |  |  |  |  |
Number of days for calculation of average closing stock price |  |  | 30 days |  |  |  |  |
Time-vested restricted stock units |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Vesting period |  |  | 3 years |  |  |  |  |
Total fair value of vested awards |  |  | $ 140.5 |  | $ 131.5 | $ 111.7 |  |
Granted (in dollars per share) | $ / shares |  |  | $ 318.87 | [3] | $ 304.44 | $ 316.32 |  |
Time-vested restricted stock units | Share-based Payment Arrangement, Tranche One |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Vesting percentage |  |  | 33.33% |  |  |  |  |
Time-vested restricted stock units | Share-based Payment Arrangement, Tranche Two |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Vesting percentage |  |  | 33.33% |  |  |  |  |
Time-vested restricted stock units | Share-based Payment Arrangement, Tranche Three |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Vesting percentage |  |  | 33.33% |  |  |  |  |
Share-based Payment Arrangement, Option |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Share based payment arrangement, term |  |  | 10 years |  |  |  |  |
Share-based Payment Arrangement, Option | Minimum |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Vesting period |  |  | 1 year |  |  |  |  |
Share-based Payment Arrangement, Option | Maximum |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Vesting period |  |  | 4 years |  |  |  |  |
Directors Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Total number of shares of common stock for issuance (in shares) | shares |  |  | 1.6 |  |  |  |  |
Ratio of total number of shares reserved under the plan |  |  | 1.5 |  |  |  |  |
2017 Omnibus Equity Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |
Ratio of total number of shares reserved under the plan |  |  | 1.5 |  |  |  |  |
Omnibus Plan number of shares authorized (in shares) | shares |  |  |  |  |  |  |  | 8.0
[1] | MSUs granted during 2020 include awards granted in conjunction with our annual awards made in February 2020 and MSUs granted in conjunction with the hiring of employees. These grants reflect the target number of shares eligible to be earned at the time of grant. MSUs granted in 2020 also reflect an adjustment based upon the final performance multiplier in relation to shares granted in 2019, 2018 and 2017.
[2] | PSUs settled in stock granted in 2020 include awards granted in conjunction with our annual awards made in February 2020 and PSUs granted in conjunction with the hiring of employees. These grants reflect the target number of shares eligible to be earned at the time of grant.
[3] | RSUs granted in 2020 primarily represent RSUs granted in conjunction with our annual awards made in February 2020 and awards made in conjunction with the hiring of new employees. RSUs granted in 2020 also include approximately 10,000 RSUs granted to our Board of Directors.

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