the facility is considered 201cdebt 201d for purposes of a support agreement between american water and awcc , which serves as a functional equivalent of a guarantee by american water of awcc 2019s payment obligations under the credit facility .
also , the company acquired an additional revolving line of credit as part of its keystone acquisition .
the total commitment under this credit facility was $ 16 million of which $ 2 million was outstanding as of december 31 , 2015 .
the following table summarizes information regarding the company 2019s aggregate credit facility commitments , letter of credit sub-limits and available funds under those revolving credit facilities , as well as outstanding amounts of commercial paper and outstanding borrowings under the respective facilities as of december 31 , 2015 and 2014 : credit facility commitment available credit facility capacity letter of credit sublimit available letter of credit capacity outstanding commercial ( net of discount ) credit line borrowing ( in millions ) december 31 , 2015 .
.
.
.
.
$ 1266 $ 1182 $ 150 $ 68 $ 626 $ 2 december 31 , 2014 .
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.
.
.
$ 1250 $ 1212 $ 150 $ 112 $ 450 $ 2014 the weighted-average interest rate on awcc short-term borrowings for the years ended december 31 , 2015 and 2014 was approximately 0.49% ( 0.49 % ) and 0.31% ( 0.31 % ) , respectively .
interest accrues on the keystone revolving line of credit daily at a rate per annum equal to 2.75% ( 2.75 % ) above the greater of the one month or one day libor .
capital structure the following table indicates the percentage of our capitalization represented by the components of our capital structure as of december 31: .

2015
2014
2013
Total common stockholders' equity
43.5%
45.2%
44.6%
Long-term debt and redeemable preferred stock at redemption value
50.6%
50.1%
49.3%
Short-term debt and current portion of long-term debt
5.9%
4.7%
6.1%
Total
100%
100%
100%

the changes in the capital structure between periods were mainly attributable to changes in outstanding commercial paper balances .
debt covenants our debt agreements contain financial and non-financial covenants .
to the extent that we are not in compliance with these covenants such an event may create an event of default under the debt agreement and we or our subsidiaries may be restricted in our ability to pay dividends , issue new debt or access our revolving credit facility .
for two of our smaller operating companies , we have informed our counterparties that we will provide only unaudited financial information at the subsidiary level , which resulted in technical non-compliance with certain of their reporting requirements under debt agreements with respect to $ 8 million of outstanding debt .
we do not believe this event will materially impact us .
our long-term debt indentures contain a number of covenants that , among other things , limit the company from issuing debt secured by the company 2019s assets , subject to certain exceptions .
our failure to comply with any of these covenants could accelerate repayment obligations .
certain long-term notes and the revolving credit facility require us to maintain a ratio of consolidated debt to consolidated capitalization ( as defined in the relevant documents ) of not more than 0.70 to 1.00 .
on december 31 , 2015 , our ratio was 0.56 to 1.00 and therefore we were in compliance with the covenant. .

Question: Analyse this data from a financial earnings document. by how much did the long-term debt and redeemable preferred stock at redemption value portion of the company's capital structure increase from 2013 to 2015?
Choices:
-0.494
0.016
0.013
0.071
1.013
Correct choice index: 2