price of these aircraft. We expect that we will invest approximately $3 billion in 2016 primarily for (1) aircraft, including deliveries of B-737-900ERs, A321-200s and A330-300s, along with advance deposit payments for these and our new A330-900neo and A350-900 orders and used E190-100 orders, as well as for (2) aircraft modifications, the majority of which relate to increasing the seat density and enhancing the cabins on our domestic fleet. We expect that the 2016 investments will be funded primarily through cash flows from operations.

Equity Investments. Our equity investments during 2015 were comprised of $450 million for China Eastern shares and $50 million for preferred shares in GOL's parent company. For additional information regarding these investments, see Note 3 of the Notes to the Consolidated Financial Statements.

During the December 2015 quarter, we announced a plan to acquire additional capital stock of Grupo Aeroméxico through a cash tender offer. Following the completion of the tender offer, when combined with our existing share ownership, we expect to own up to 49% of Grupo Aeroméxico's outstanding shares. This approximately $750 million capital investment is subject to regulatory approvals and the tender offer would likely commence in the June 2016 quarter.

Financing Activities

Debt and Capital Leases. The principal amount of debt and capital leases has declined from $13.2 billion at the beginning of 2013 to $8.5 billion at

December 31, 2015 . Since December 31, 2009, we have reduced our principal amount of debt and capital leases by $9.8 billion. These debt reductions also serve to reduce our total future interest expense. We have focused on reducing our total debt in recent years as part of our strategy to strengthen our balance sheet. As a result, we received upgrades to our credit rating by all three major rating agencies during 2015, to the following ratings.

Continued improvement in our credit ratings to investment grade would likely result in lower costs of borrowing, among other things.

In connection with the retirement and termination of the outstanding loans under our existing $2.5 billion Senior Secured Credit Financing Facilities (due April 2016 and April 2017), we completed refinancing transactions in August 2015 with new debt consisting of the Senior Secured Credit Facilities ($2.0 billion) and the 2015-1 EETC ($500 million). The Senior Secured Credit Facilities consist of a $1.5 billion Revolving Credit Facility and a $500 million Term Loan Facility.

Capital Returns to Shareholders. Since 2013, our Board of Directors has implemented three programs to return capital to shareholders through quarterly dividends and share repurchases. Since first implementing our quarterly dividend in 2013, we have increased the dividend per share by 50% annually, and paid $712 million in total dividends, including $359 million in 2015. Through dividends and share repurchases, we have returned over $4 billion to shareholders since 2013, while reducing outstanding shares by approximately 9% compared to the beginning of 2013. During 2015 alone, we repurchased and retired 48.4 million shares at a cost of $2.2 billion.

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