The guaranteed liability for the fixed indexed annuity GMWB and GMDB increased in both periods, excluding unlock, but increased $33.1 million for the year ended December 31, 2014 and increased $60.5 million for the year ended December 31, 2013. The reduction in the current year expense is primarily driven by realized capital losses on the derivative investments used to hedge this business, which generally positively impact the guaranteed benefit liabilities.
We also measure, manage and monitor market risk associated with our investments, both those backing insurance liabilities and those supporting surplus. This process primarily involves Corporate Portfolio Management. This organization makes recommendations and reports results to our Investment Policy Committee, chaired by the Chief Investment Officer. Please refer to the sections that follow, including “Debt and Equity Securities,” following this discussion of Enterprise Risk Management, for more information on our investment risk exposures. Within the parameters specified in our investment policy, we regularly refine our allocations based on factors including ratings, duration and type of fixed income security to appropriately balance market risk exposure and expected return.
The Company estimates that the annualized net investment income yield on its fixed income securities was approximately 4.3% during the year ended December 31, 2014. The average investment rate on fixed income securities purchases during the year ended December 31, 2014 was approximately 4.0% on total purchases of approximately $1.1 billion. Management estimates that proceeds from maturities, calls and prepayments of approximately $220 million is expected to be available for reinvestment over the next 12 months, before considering new deposits and premiums and other cash flow uses. Assuming such amounts are reinvested at new money interest rates prevailing at December 31, 2014, we estimate that would reduce net investment income by less than $3 million during the next 12 months. The estimated impact is subject to change as the composition of the portfolio changes through normal portfolio management and other factors.
Cash flows used for operating activities decreased by $47.1 million during the year ended December 31, 2014 compared to the year ended December 31, 2013. This decrease was driven by lower death benefits paid for universal life during 2014 in conjunction with reduced audit and consulting fees related to the restatement of our prior period financial statements. Partially offsetting this decrease was increased commission paid related to higher sales of fixed indexed annuity products.
Cash flows used for investing activities increased $170.0 million during the year ended December 31, 2014 compared to the year ended December 31, 2013 as a result of of an increase in purchases of available-for-sale securities and short-term investments. This change is primarily driven by more cash being provided by operating activities, namely due to a reduction in death benefits and professional fees paid. Partially offsetting this increase were increased sales and maturities of short-term investments during the period.
The increase in the accumulated deficit was partially offset by an increase in accumulated other comprehensive income of $16.7 million. The increase in accumulated other comprehensive income was driven primarily by net unrealized gains on investments, and the related offsetting impacts, due to decreases in interest rates during 2014.
See Note 16 to our financial statements under “Item 8: Financial Statements and Supplementary Data” in this Form 10-K for additional information.