Share-Based Incentives Class B rollforward (Details) - shares	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding, beginning of year	100,000,000
Shares outstanding, end of year	100,000,000	100,000,000
Class B Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding, beginning of year	281,768	345,644
Granted	167,202	117,929
Purchased	38,838	18,875
Repurchased	(213,144)	(200,680)
Net expirations and exercises	0
Shares outstanding, end of year	274,664	281,768
Restricted Class B shares \| Class B Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding, beginning of year	179,332	161,810
Granted	167,202	117,929
Purchased	0	0
Repurchased	(129,583)	(100,407)
Expiration of restricted period	(27,785)
Shares outstanding, end of year	189,166	179,332
Unrestricted Class B shares \| Class B Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding, beginning of year	102,436	183,834
Granted	0	0
Purchased	38,838	18,875
Repurchased	(83,561)	(100,273)
Exercised	27,785
Shares outstanding, end of year	85,498	102,436

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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- Definition

Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Number of shares issued under share-based payment arrangement.

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Number of share options (or share units) exercised during the current period.

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Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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