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v3.19.3.a.u2

Stock Transactions and Unit Redemptions - Changes in Shares of Class A Common Stock Outstanding (Parenthetical) (Detail) - shares shares in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018
Limited Partnership [Member] |  |
Class of Stock [Line Items] |  |
Number of units redeemed and cancelled for exchange | 11.5 | 7.6
Class A Common Stock [Member] |  |
Class of Stock [Line Items] |  |
Common stock, shares issued | 10.1 | 6.8

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