Share Repurchase Programs
On December 1, 2014, the Company announced the "Capital Allocation Policy" under which the Company intends to return to stockholders approximately 80 percent of free cash flow, less repayments of long-term debt, subject to a variety of factors, including the strategic plans, market and economic conditions and the discretion of the Company’s board of directors. For the purposes of the Capital Allocation Policy, the Company defines "free cash flow" as net cash provided by operating activities less purchases of property, plant and equipment.
On December 1, 2014, the Company announced the 2014 Share Repurchase Program (the "2014 Share Repurchase Program") pursuant to the Capital Allocation Policy. Under the Company’s 2014 Share Repurchase Program, the Company had the ability to repurchase up to $ 1.0 billion (exclusive of fees, commissions and other expenses) of the Company’s common stock over a period of four years from December 1, 2014, subject to certain contingencies.
The 2014 Share Repurchase Program, which did not require the Company to purchase any particular amount of common stock and was subject to the discretion of the board of directors, expired on November 30, 2018 with approximately $288.2 million remaining unutilized.
The Company repurchased common stock worth approximately $315.0 million and $25.0 million under the 2014 Share Repurchase Program during the years ended December 31, 2018 and December 31, 2017, respectively.
On November 15, 2018, the Company announced the 2018 Share Repurchase Program (the "2018 Share Repurchase Program") pursuant to the Capital Allocation Policy. Under the 2018 Share Repurchase Program, the Company is authorized to repurchase up to $ 1.5 billion of its common shares from December 1, 2018 through December 31, 2022, exclusive of any fees, commissions or other expenses.
The Company may repurchase its common stock from time to time in privately negotiated transactions or open market transactions, including pursuant to a trading plan in accordance with Rule 10b5-1 and Rule 10b-18 of the Exchange Act, or by any combination of such methods or other methods.
The timing of any repurchases and the actual number of shares repurchased will depend on a variety of factors, including the Company’s stock price, corporate and regulatory requirements, restrictions under the Company’s debt obligations and other market and economic conditions. There were $138.9 million in repurchases of the Company's common stock under the 2018 Share Repurchase Program during the year ended December 31, 2019. As of December 31, 2019, the remaining authorized amount under the 2018 Share Repurchase Program was $1,361.1 million.
Information relating to the Company's 2018 and 2014 Share Repurchase Programs is as follows (in millions, except per share data):
(1) None of these shares had been reissued or retired as of December 31, 2019, but may be reissued or retired by the Company at a later date.

Year ended December 31,
2019
2018
2017
Number of repurchased shares (1)
7.8
16.8
1.6
Aggregate purchase price
$138.9
$315.0
$25.0
Fees, commissions and other expenses
0.1
0.3
—
Total cash used for share repurchases
$139.0
$315.3
$25.0
Weighted-average purchase price per share
$17.89
$18.78
$15.35
Available for future purchases at period end
$1,361.1
$1,500.0
$603.2


Question: Analyse this data from a financial earnings document. What is the change in Number of repurchased shares from December 31, 2018 to 2019?
Choices:
8
-15
-9
13
131
Correct choice index: 2