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Stock-Based Compensation Plans (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions |  | 12 Months Ended
--- | --- | ---
Mar. 26, 2012 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Total authorized shares for plan issuance |  | 2,000,000.0 |  |
Shares available for issuance |  | 116,031 |  |
Fair value of shares vested |  | $ 5.1 | $ 7.9 | $ 4.8
Intrinsic value of restricted stock units exercised |  | $ 7.6 | $ 36.9 | $ 0.5
Weighted average recognition period |  | 2 years 2 months 12 days |  |
Restricted stock outstanding excluded from calculation of diluted net income per share |  | 0 | 0 | 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross |  | 622,000 |  |
Share-based Payment Arrangement, Option, Exercise Price Range, Exercisable, Weighted Average Exercise Price |  | $ 333.94 |  |
Restricted Stock [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Weighted average fair value of shares granted |  |  | $ 441.54 | $ 317.87
Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Weighted average fair value of shares granted |  | $ 436.89 | $ 453.64 | $ 363.11
Restricted stock units converted to common stock, shares |  | 21,971 |  |
Fifteen Year Vesting [Member] | Restricted Stock [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Vesting period |  | 15 years |  |
Ten Year Vesting [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Vesting period |  | 10 years |  |
Five Year Vesting [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Vesting period |  | 5 years |  |
Three Year Vesting [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Vesting period |  | 3 years |  |
Four Year Vesting [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Vesting period |  | 4 years |  |
Incentive Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of additional shares authorized for issuance | 500,000 |  |  |

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