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Changes in Capital Structure - Narrative (Details) - USD ($) |  | 1 Months Ended | 3 Months Ended |  |
--- | --- | --- | --- | --- | ---
May 02, 2019 | Apr. 30, 2019 | Mar. 31, 2019 | Mar. 12, 2019 | Mar. 31, 2019 | Mar. 31, 2018 | Feb. 28, 2019 | Dec. 31, 2018
Capital Structure |  |  |  |  |  |  |  |
Common stock, shares authorized (in shares) |  |  | 500,000,000 |  | 500,000,000 |  |  | 500,000,000
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% |  |  |  |  |
Shares repurchased, value |  |  |  |  | $ 749,000,000 | $ 93,000,000 |  |
Total number of shares purchased (in shares) |  |  |  |  | 17,608,957 |  |  |
Additional Paid-in Capital |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |
Shares repurchased, value |  |  |  |  | $ 10,000,000 |  |  |
Accelerated Share Repurchase Program |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |
Shares repurchased, value |  |  |  | $ 390,000,000 |  |  |  |
Stock repurchase program, authorized amount |  |  |  |  |  |  | $ 400,000,000 |
Shares repurchased (in shares) |  |  |  | 9,086,903 |  |  |  |
Accelerated Share Repurchase Program | Subsequent Event |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |
Shares repurchased (in shares) |  | 351,768 |  |  |  |  |  |
Average price paid per share (in usd per share) |  | $ 42.38 |  |  |  |  |  |
Accelerated Share Repurchase Program | Additional Paid-in Capital | Subsequent Event |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |
Remaining amount recorded in additional paid in capital |  | $ 10,000,000 |  |  |  |  |  |
2018 Capital Allocation Plan |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |
Shares repurchased, value |  |  |  |  | $ 250,000,000 |  |  |
Total number of shares purchased (in shares) |  |  |  |  | 6,153,415 |  |  |
Amounts paid for shares purchased |  |  |  |  | $ 250,000,000 |  |  |
Capital Allocation Plan, Accelerated Repurchase Agreement February 2019 |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |
Total number of shares purchased (in shares) |  |  |  | 9,086,903 |  |  |  |
Amounts paid for shares purchased |  |  |  | $ 400,000,000 |  |  |  |
Capital Allocation Plan, Accelerated Repurchase Agreement February 2019 | Subsequent Event |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |
Total number of shares purchased (in shares) |  | 351,768 |  |  |  |  |  |
Amounts paid for shares purchased |  | $ 0 |  |  |  |  |  |
2019 Capital Allocation Plan |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |
Total number of shares purchased (in shares) |  |  | 2,368,639 |  |  |  |  |
Amounts paid for shares purchased |  |  | $ 99,000,000 |  |  |  |  |
2019 Capital Allocation Plan | Subsequent Event |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |
Total number of shares purchased (in shares) |  | 39,140 |  |  |  |  |  |
Amounts paid for shares purchased |  | $ 1,000,000 |  |  |  |  |  |
Capital Allocation Plan |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |
Stock repurchase program, authorized amount |  |  |  |  |  |  | $ 1,000,000,000.0 |
Total number of shares purchased (in shares) |  |  |  |  | 17,608,957 |  |  |
Amounts paid for shares purchased |  |  |  |  | $ 749,000,000 |  |  |
Capital Allocation Plan | Subsequent Event |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |
Shares repurchased, value | $ 500,000,000 |  |  |  |  |  |  |
Average price paid per share (in usd per share) | $ 42.21 |  |  |  |  |  |  |
Total number of shares purchased (in shares) | 17,999,865 |  |  |  |  |  |  |
Amounts paid for shares purchased | $ 750,000,000 |  |  |  |  |  |  |

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