Stockholders' Equity of the Company - Stock Repurchase Program (Details)	9 Months Ended	12 Months Ended
	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