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Stockholders' Equity - Share Repurchase Activity (Details) - Common Stock - $ / shares
shares in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Class of Stock [Line Items]      
Shares repurchased (in shares) 4.1 3.3 2.4
Average price of stock repurchased (in dollars per share) $ 88.73 $ 150.31 $ 173.19