The amortized cost, gross unrealized gains and losses, and fair value of securities available for sale and securities held to maturity are as follows:

A summary of securities with unrealized losses, aggregated by category and period of continuous unrealized loss, is as follows:

Unrealized losses in securities available for sale of $52 million as of March 31, 2013, were concentrated in non-agency residential mortgage-backed securities. Included in non-agency residential mortgage-backed securities are securities collateralized by loans that are considered to be “Prime” (defined as loans to borrowers with a Fair Isaac Corporation (FICO) credit score of 620 or higher at origination), and “Alt-A” (defined as Prime loans with reduced documentation at origination). At March 31, 2013, the amortized cost and fair value of Alt-A residential mortgage-backed securities were $295 million and $269 million, respectively.

Certain Alt-A and Prime residential mortgage-backed securities experienced continued credit deterioration in the first quarter of 2013. Based on the Company’s cash flow projections, management determined that it does not expect to recover all of the amortized cost of these securities and therefore determined that these securities were other-than-temporarily impaired (OTTI). The Company employs a buy and hold strategy relative to its mortgage-related securities, and does not intend to sell these securities and will not be required to sell these securities before anticipated recovery of the unrealized losses on these securities. Further, the Company has adequate liquidity at March 31, 2013, with cash and cash equivalents totaling $6.9 billion, a loan-to-deposit ratio of 14%, adequate access to short-term borrowing facilities and regulatory capital ratios in excess of “well capitalized” levels. Because the Company does not intend to sell these securities and it is not “more likely than not” that the Company will be required to sell these securities, the Company recognized an impairment charge equal to the securities’ expected credit losses of $4 million during the first quarter of 2013. The expected credit losses were measured as the difference between the present value of expected cash flows and the amortized cost of the securities. Further deterioration in the performance of the underlying loans in the Company’s non-agency residential mortgage-backed securities portfolio could result in the recognition of additional impairment losses.

The following table is a rollforward of the amount of credit losses recognized in earnings for OTTI securities held by the Company during the period for which a portion of the impairment was recognized in other comprehensive income:

The maturities of securities available for sale and securities held to maturity at March 31, 2013, are as follows:

There were no sales of securities available for sale in the first quarter of 2013. Proceeds received from sales of securities available for sale were $250 million in the first quarter of 2012. There were no gross realized gains or losses from sales of securities available for sale in the first quarter of 2012.