We expect to realize the full year benefit in 2018 of business commenced during 2017 in Florida, Maryland, Missouri and Nevada, as discussed above.
In January 2018, our Illinois subsidiary, IlliniCare Health, began operating under a state-wide contract for the Medicaid Managed Care Program including children who are in need through the Department of Children and Family Services (DCFS)/Youth in Care by the Illinois Department of Healthcare and Family Services (HFS). Implementation dates vary by region and will be fully implemented statewide by April 2018. Foster Care will be implemented by July 2018.
In addition, we will no longer be serving Medicaid members in Massachusetts.
The increases above are partially offset by a decrease in acquisition related expenses of $214 million.
The increase in investment income in 2016 reflects an increase in investment balances over 2015, primarily due to the acquisition of Health Net. Interest expense increased during the year ended December 31, 2016 by $174 million primarily reflecting the issuance of an additional $2,400 million in Senior Notes in February 2016 in connection with the financing of the Health Net transaction. Interest expense also increased due to the issuance of an additional $500 million in Senior Notes in June 2016, the assumption of Health Net's $400 million in Senior Notes, and the issuance of the $1,200 million in Senior Notes in November 2016. These increases were partially offset by the redemption of the Centene $425 million 5.75% Senior Notes and the Health Net $400 million 6.375% Senior Notes in November 2016 and December 2016, respectively. In addition, we incurred $11 million associated with the early redemption of the Centene 5.75% Senior Notes due 2017 and the Health Net 6.375% Senior Notes due 2017, which was recorded in interest expense.
The indentures governing our various maturities of senior notes contain non-financial and financial covenants of Centene Corporation, including requirements of a minimum fixed charge coverage ratio. As of December 31, 2017, we were in compliance with all covenants.
Investments with original maturities of three months or less are considered to be cash equivalents. Cash equivalents consist of money market funds, bank certificates of deposit and savings accounts.
In August 2016, the Financial Accounting Standards Board (FASB) issued an Accounting Standard Update (ASU) which clarifies how entities should classify certain cash receipts and cash payments on the statement of cash flows. The new guidance also clarifies how the predominance principle should be applied when cash receipts and cash payments have aspects of more than one class of cash flows. The Company early adopted the new guidance in the fourth quarter of 2017. The new guidance did not have a material impact on the Company's consolidated financial statements.
Debt is required to be measured at fair value under the acquisition method of accounting. The fair value of Health Net's $400 million Senior Notes assumed in the acquisition was $418 million. The $18 million increase was initially being amortized as a reduction to interest expense over the remaining life of the debt; however, in November 2016, this debt was redeemed. See further discussion in Note 11, Debt.
From the acquisition date through December 31, 2016, the Company's Consolidated Statements of Operations include total Health Net revenues of $13,454 million. It is impracticable to determine the effect on net income resulting from the Health Net acquisition for the year ended December 31, 2016, as the Company immediately integrated Health Net into its ongoing operations.
In June 2016, the Company issued an additional $500 million in aggregate principal amount of 4.75% Senior Notes due 2022 ($500 Million Add-on Notes) at a premium to yield of 4.41%. The $500 Million Add-on Notes were offered as additional debt securities under the indenture governing the $500 million in aggregate principal amount of 4.75% Senior Notes issued in April 2014. The Company used the net proceeds of the offering to repay amounts outstanding under its Revolving Credit Facility and to pay offering related fees and expenses.
Uncertain tax positions increased $143 million to reflect the impact of a multi-year reserve for deductions related to domestic production activities. As of December 31, 2017, $225 million of unrecognized tax benefits would impact the Company's effective tax rate in future periods, if recognized. The Company believes it is reasonably possible that its liability for unrecognized tax benefits will decrease in the next twelve months by $8 million as a result of the expiration of statutes of limitations in certain jurisdictions.
The table above excludes interest, net of related tax benefits, which is treated as income tax expense (benefit) under the Company's accounting policy. For the year ended December 31, 2017, the Company recognized net interest expense and penalties related to uncertain positions of $4 million. The Company had $9 million and $5 million of accrued interest and penalties for uncertain tax positions as of December 31, 2017 and 2016, respectively.
The Company files tax returns for federal as well as numerous state tax jurisdictions. As of December 31, 2017, Health Net is under federal examination for tax years 2011 through its final return in 2016. Additionally, Centene's tax returns for years 2014 through 2016 are subject to federal examination.