For the year ended December 31, 2013 the gain on U.S. GMWB related derivatives, net, was primarily related to gains of $203 from revaluing the liability for living benefits largely driven by favorable policyholder behavior related to increased full surrenders and gains of $38 due to liability assumption updates for partial lapses and withdrawal rates. The loss on the U.S. macro hedge program for the year ended December 31, 2013 was primarily driven by losses of $114 due to an improvement in domestic equity markets, losses of $56 related to an increase in interest rates, and losses of $31 related to a decrease in equity market volatility. The loss on the international program for the year ended December 31, 2013 was primarily driven by an improvement in global equity markets and depreciation of the Japanese yen in relation to the euro.
Goodwill balances are reviewed for impairment at least annually or more frequently if events occur or circumstances change that would indicate that a triggering event for a potential impairment has occurred.
A decline in interest rates results in certain mortgage-backed and municipal securities being more susceptible to paydowns and prepayments or calls. During such periods, the Company generally will not be able to reinvest the proceeds at comparable yields. Lower interest rates will also likely result in lower net investment income, increased hedging cost associated with variable annuities and, if declines are sustained for a long period of time, it may subject the Company to reinvestment risk, higher pension costs expense and possibly reduced profit margins associated with guaranteed crediting rates on certain products. Conversely, the fair value of the investment portfolio will increase when interest rates decline and the Company’s interest expense will be lower on its variable rate debt obligations.
As of December 31, 2013, the Company's only exposure to any credit concentration risk of a single issuer or counterparty greater than 10% of the Company's stockholders' equity, other than the U.S. government and certain U.S. government securities, was the Government of Japan and Prudential. The Government of Japan securities represented $853, or 10% of stockholders' equity, and 2% of total invested assets. For further discussion of concentration of credit risk, see the Concentration of Credit Risk section in Note 4 - Investments and Derivative Instruments of Notes to Consolidated Financial Statements. The net unsecured reinsurance recoverable from Prudential of $2.4 billion represented approximately 29% of stockholder's equity. For further discussion of reinsurance recoverables, see Note 5 - Reinsurance of Notes to Consolidated Financial Statements.
As of December 31, 2013 and 2012, the notional amount related to credit derivatives that purchase credit protection was $0.6 billion and $1.9 billion, respectively, while the fair value was $1 and $23. As of December 31, 2013 and 2012, the credit derivatives that purchase credit protection included notional of $0.4 billion and fair value of $5 and $28, respectively, that are part of the international program hedging instruments. As of December 31, 2013 and 2012, the notional amount related to credit derivatives that assume credit risk was $1.5 billion and $2.0 billion, respectively, while the fair value was $27 and $(8), respectively. For further information on credit derivatives, see Note 4 - Investments and Derivative Instruments of Notes to Consolidated Financial Statements.
Total general account contractholder obligations are supported by $38 billion of cash and total general account invested assets, excluding equity securities, trading, which includes a significant short-term investment position, as depicted below, to meet liquidity needs.
Net cash provided by investing activities in 2013 primarily relates to net proceeds of available-for-sale securities of $4.7 billion and proceeds on business sold of $745 partially offset by payments on derivatives of $1.9 billion. Net cash used for investing activities in 2012 primarily relates to net payments on derivatives of $2.2 billion, net purchases of mortgage loans of of $750, and net purchases of partnerships of $307, partially offset by net proceeds of available-for-sale securities of $1.2 billion.