Core income was $735 million, or $2.70 per share, and net income for the year was $690 million, or $2.53 per share.
This compares to $979 million and $1 billion in 2019, respectively.
The shortfall from the prior year primarily attributed to the impact of the elevated pre-tax catastrophe losses of $550 million, which included our reserve charge for the pandemic of $195 million that we announced in the second quarter of 2020 as compared to $179 million of catastrophe losses in 2019.
On the other hand, our P&C underlying underwriting profit for the full-year increased 38% to $498 million as the underlying combined ratio improved 1.7 points to 93.1%.
Our underlying loss ratio improved 0.8 points from 2019.
The expense ratio improved 0.9 points from 2019 to 32.6%, which reflected our disciplined approach to managing expenses as we grow the business and continue to make meaningful investments in talent, technology and analytics.
The all-in combined ratio was 100.9% with 7.7 points of catastrophe losses and flat prior period development.
Gross written premium growth ex-captives grew 9% in 2020 despite the impacts of the economic downturn, which reduced our exposure almost 3 points from the prior year.
Net written premium increased 6% for the full-year.
We successfully achieved rate increases of 11% for the full-year, more than double our 2019 rate increases, and new business was up 6% for the year.
The 11% of written rate we achieved in 2020 was 8 points on an earned basis for the full-year, while our long run loss cost trends were about 4 points.
Core income for the quarter was a record $335 million, $1.23 per share, an increase of $70 million over the prior year fourth quarter.
Net income for the quarter was $387 million, or $1.42 per share, and was an increase of $114 million over 2019's fourth quarter.
The P&C underlying combined ratio was 92.7%, a significant improvement over last year's fourth quarter results and in line with Q3 results, both of which are the best two underlying combined ratios CNA has had in over 10 years.
The all-in combined ratio was 93.5%, slightly more than 2 points of improvement compared to the fourth quarter a year ago, driven by commercial, which improved 4.4 points to 96.2% and international, which improved 3.4 points to 96.9%.
Although specialty had less favorable prior period development in the fourth quarter a year ago, they had a very strong combined ratio of 89.4%.
Pre-tax catastrophe losses were benign at $14 million, or 0.8 points of the combined ratio.
Our estimated ultimate losses from COVID-19 are unchanged at $195 million as claim activity continues to unfold slowly, as we expected.
The underlying loss ratio was 60.5% for the quarter, a 0.4 point year-over-year improvement and consistent with Q3.
Specialty was 60%, commercial was 61.1%, and international was 60.1%.
In the fourth quarter, the expense ratio was 32%, 1.7 points better than the prior year quarter as we maintained a disciplined approach to managing expenses as we continue to grow the business.
Gross written premium ex our captive business grew 15% in the quarter with significant contributions across all operating segments, with specialty at plus 17% and commercial at plus 13%.
International was also strong at plus 14%, fueled by strong rate in the quarter in our London operation and strong rate and new business growth in our Canadian operations.
Net written premium for total P&C increased 12% in the quarter.
In the quarter, the hardening market persisted as evidenced by our continued double-digit rate achievement of plus 12%, while increasing our retention by 3 points to 85% from the third quarter.
We achieved strong rate across the board with specialty at plus 13%, commercial at plus 12%, and international at plus 18%.
New business growth was strong in the quarter, 17% higher compared to last year's fourth quarter.
Specialty grew 23% and commercial 22%, while international remained slightly negative.
Finally, we completed our annual asbestos and pollution reserve review, which resulted in a non-economic after-tax charge of $39 million, which compares to last year's after-tax charge of $48 million, and we also had positive core income of $26 million from our life and group operations.
Core income for the quarter was a record at $335 million, 26% higher than the prior year quarter results.
With a core ROE of 11.4% for the period, we are certainly pleased with the close to 2020 and the significant progress made to build upon our underlying underwriting profitability.
Our fourth quarter expense ratio of 32% reflects significant progress on a year-over-year basis, as well as on a sequential quarter basis during 2020.
The expense ratio improvement was reflected in all three of our P&C business segments, especially in international notably recording improvements of 2 and 3 points, respectively, versus the prior year quarter.
Turning to net prior period development and reserves, for the fourth quarter overall P&C net prior period development was flat compared to 2.2 points of favorable development in Q4 2019.
For the full-year 2020, overall development was essentially flat versus 0.7 points of favorable development in 2019.
This segment produced core income of $26 million in the quarter and $9 million for the full-year.
This compares with Q4 2019 loss of $4 million and a full-year 2019 loss of $109 million.
Our Corporate segment produced a core loss of $60 million in the fourth quarter and $108 million for the full-year.
This compares to a $68 million loss in Q4 2019 and $102 million loss for the full-year 2019.
The results of the review included a non-economic after-tax charge of $39 million driven by the strengthening of reserves associated with higher defense and indemnity costs on existing claims, and this compares to last year's non-economic charge of $48 million.
Following this review, we have incurred cumulative losses of $3.3 billion, well within the $4 billion limit of our loss portfolio transfer cover that we purchased in 2010, and paid losses are now at $2.1 billion.
This non-core portfolio has been in runoff for over 10 years and the transaction enables us to strengthen our focus on going forward operations while reducing potential future reserve volatility.
Pre-tax net investment income was $555 million in the fourth quarter, compared with $545 million in the prior year quarter.
As a point of reference, pre-tax effective yield on our fixed income holdings was 4.4% at Q4 2020 compared to 4.7% as of Q4 2019.
Pre-tax net investment income for the full-year was $1.9 billion, compared with $2.1 billion in the prior year.
While lower interest rates have certainly been a headwind for our net investment income, it's also driven the increase of our unrealized gain position on our fixed income portfolio, which stood at $5.7 billion at year end, up from $5 billion at the end of the third quarter and $4.1 billion at the end of 2019.
Fixed income invested assets that support our P&C liabilities had an effective duration of 4.5 years at quarter end.
The effective duration of the fixed income assets that support our Life & Group liabilities was 9.2 years at quarter end.
At quarter end, shareholders' equity was $12.7 billion, or $46.82 per share, reflective of the increase in our unrealized gain position during the quarter.
Shareholders' equity excluding accumulated other comprehensive income was $11.9 billion, or $43.86 per share.
Book value per share ex-AOCI and excluding the impact of dividends paid has grown by 6% over the last year.
We have a conservative capital structure with a leverage ratio below 18% and continue to maintain capital above target levels in support of our ratings.
In the fourth quarter, operating cash flow was strong at $367 million, compared to $160 million during Q4 2019.
On a full-year basis, operating cash flow was $1.8 billion versus $1.1 billion for 2019, a significant increase substantially driven by the improvement in our current accident year underwriting profitability and a lower level of paid losses.
Finally, we are pleased to announce an increase in our regular quarterly dividend to $0.38.
In addition, notwithstanding an extraordinary year in 2020, including the elevated impact of catastrophe on our results, we were pleased to declare a special dividend of $0.75 per share.

Summary:
Core income was $735 million, or $2.70 per share, and net income for the year was $690 million, or $2.53 per share.
Core income for the quarter was a record $335 million, $1.23 per share, an increase of $70 million over the prior year fourth quarter.
Net income for the quarter was $387 million, or $1.42 per share, and was an increase of $114 million over 2019's fourth quarter.
At quarter end, shareholders' equity was $12.7 billion, or $46.82 per share, reflective of the increase in our unrealized gain position during the quarter.