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Stockholders' Equity of the Company - Stock Repurchase Program (Details) | 9 Months Ended | 12 Months Ended |  |
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Sep. 30, 2021 USD ($) increase $ / shares shares | Dec. 31, 2020 USD ($) $ / shares shares | Dec. 31, 2019 USD ($) $ / shares shares | Dec. 31, 2018 USD ($) $ / shares shares | Dec. 31, 2017 USD ($) $ / shares shares | Jun. 30, 2018 USD ($) | Aug. 31, 2016 USD ($)
Class of Stock [Line Items] |  |  |  |  |  |  |
Share repurchased (in shares) | shares | 3,797,082 | 8,529,279 | 4,465,857 | 9,468,617 | 8,105,881 |  |
Average price paid per share (in dollars per share) | $ / shares | $ 72.89 | $ 62.39 | $ 86.06 | $ 99.03 | $ 104.61 |  |
2016 Repurchase Program |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Stock repurchase program, authorized amount | $ |  | $ 500,000,000 | $ 500,000,000 | $ 500,000,000 | $ 500,000,000 | $ 500,000,000 | $ 1,000,000,000
Number of increases to share repurchase program | increase | 5 |  |  |  |  |  |
Stock repurchase program, authorized amount | $ | $ 3,500,000,000 |  |  |  |  |  |
Share repurchased (in shares) | shares | 34,366,716 | 30,569,634 | 22,040,355 | 17,574,498 | 8,105,881 |  |

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- Definition Amount of stock repurchase plan authorized. + References No definition available. + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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