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Changes in Capital Structure - Narrative (Details) - USD ($) |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | ---
May 24, 2018 | Jan. 01, 2018 | Aug. 02, 2018 | Jul. 31, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Jun. 30, 2018 | Feb. 28, 2018 | Dec. 31, 2017
Capital Structure |  |  |  |  |  |  |  |  |
Common stock, shares authorized (in shares) |  |  |  |  | 500,000,000 |  | 500,000,000 |  | 500,000,000
Shares issued under ESPP (in shares) |  | 175,862 |  |  |  |  |  |  |
Stock repurchase program, authorized amount | $ 354,000,000 |  |  |  |  |  |  |  |
Stock repurchase program, amount, beginning immediately |  |  |  |  |  |  |  | $ 500,000,000 |
Total number of shares purchased (in shares) |  |  |  |  |  |  | 14,863,301 |  |
Commissions per share (in dollars per share) |  |  |  |  | $ 0.01 |  |  |  |
Shares received under ASR Agreement (in shares) | 9,969,023 |  |  |  |  |  |  |  |
Treasury |  |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |  |
Shares issued under ESPP (in shares) |  | 175,862 |  |  |  |  |  |  |
Total number of shares purchased (in shares) |  |  |  |  |  |  | 14,863,301 |  |
Accelerated Share Repurchase Program |  |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |  |
Value of shares received | $ 343,000,000 |  |  |  |  |  |  |  |
Accelerated Share Repurchase Program | Additional Paid-in Capital |  |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |  |
Remaining amount recorded in additional paid in capital | $ 11,000,000 |  |  |  |  |  |  |  |
Subsequent Event |  |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |  |
Average price paid per share (in dollars per share) |  |  | $ 31.80 |  |  |  |  |  |
Commissions per share (in dollars per share) |  |  | $ 0.01 |  |  |  |  |  |
Subsequent Event | Accelerated Share Repurchase Program |  |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |  |
Shares received under ASR Agreement (in shares) |  |  |  | 860,880 |  |  |  |  |
Average price paid per share under ASR Agreement (in dollars per share) |  |  |  | $ 32.69 |  |  |  |  |
Subsequent Event | Accelerated Share Repurchase Program | Treasury |  |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |  |
Remaining amount recorded in additional paid in capital |  |  |  | $ 11,000,000 |  |  |  |  |
Capital Allocation Plan |  |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |  |
Stock repurchase program, authorized amount |  |  |  |  |  |  |  | $ 1,000,000,000 |
Total number of shares purchased (in shares) |  |  |  |  | 11,748,553 | 3,114,748 | 14,863,301 |  |
Amounts paid for shares purchased |  |  |  |  | $ 407,000,000 | $ 93,000,000 | $ 500,000,000 |  |
Capital Allocation Plan | Subsequent Event |  |  |  |  |  |  |  |  |
Capital Structure |  |  |  |  |  |  |  |  |
Total number of shares purchased (in shares) |  |  | 15,724,181 | 860,880 |  |  |  |  |
Amounts paid for shares purchased |  |  | $ 500,000,000 | $ 0 |  |  |  |  |

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