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Changes in Capital Structure - Narrative (Details) - USD ($) | 1 Months Ended | 2 Months Ended | 3 Months Ended |
--- | --- | --- | --- | ---
Oct. 31, 2019 | Apr. 30, 2019 | Mar. 31, 2019 | Feb. 28, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2018
Capital Structure |  |  |  |  |  |  |  |  |  |  |
Common stock, shares authorized (in shares) |  |  |  |  | 500,000,000 |  |  |  |  |  | 500,000,000
Stock repurchase program, authorized amount |  |  |  | $ 400,000,000 |  |  |  |  |  |  |
Shares repurchased, value |  |  |  |  | $ 234,000,000 | $ 305,000,000 | $ 749,000,000 | $ 500,000,000 | $ 407,000,000 | $ 93,000,000 |
Employee Stock Purchase Plan, minimum percentage of eligible compensation to purchase shares |  |  | 1.00% |  |  |  |  |  |  |  |
Employee Stock Purchase Plan, maximum percentage of eligible compensation |  |  | 10.00% |  |  |  |  |  |  |  |
Employee Stock Purchase Plan, exercise price as percentage of fair value |  |  | 95.00% |  |  |  |  |  |  |  |
Subsequent Event |  |  |  |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |  |  |  |
Shares issued to employee accounts (in shares) | 46,128 |  |  |  |  |  |  |  |  |  |
Additional Paid-in Capital |  |  |  |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |  |  |  |
Shares repurchased, value |  |  |  |  |  | $ (10,000,000) | $ 10,000,000 | $ 37,000,000 | $ 11,000,000 |  |
Accelerated Share Repurchase Program |  |  |  |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |  |  |  |
Shares repurchased (in shares) |  | 351,768 | 9,086,903 |  |  |  |  |  |  |  |
Shares repurchased, value |  |  | $ 390,000,000 |  |  |  |  |  |  |  |
Average price paid per share (in usd per share) |  | $ 42.38 |  |  |  |  |  |  |  |  |
Accelerated Share Repurchase Program | Additional Paid-in Capital |  |  |  |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |  |  |  |
Remaining amount recorded in additional paid in capital |  | $ 10,000,000 |  |  |  |  |  |  |  |  |
2018 Plan |  |  |  |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |  |  |  |
Average price paid per share (in usd per share) |  |  |  | $ 40,610,000 |  |  |  |  |  |  |
2019 Plan |  |  |  |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |  |  |  |
Stock repurchase program, authorized amount |  |  |  | $ 1,000,000,000 |  |  |  |  |  |  |

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