OTHER ASSETS

Included in other assets were the following:



	December 31,
	2016		2015
	($ in millions)
Investments in non-consolidated affiliates	$	26.7	$	25.0
Deferred debt issuance costs	2.6		3.3
Tax-related receivables	17.5		1.5
Interest rate swaps	7.7		—
Supply contracts	566.7		406.5
Other	23.2		18.3
Other assets	$	644.4	$	454.6

In connection with the Acquisition, Olin and TDCC have agreed to enter into arrangements for the long-term supply of ethylene by TDCC to Olin, pursuant to which, among other things, Olin has made upfront payments of $433.5 million upon the Closing Date in order to receive ethylene at producer economics and for certain reservation fees for the option to obtain additional future ethylene supply at producer economics. The fair value of the long-term supply contracts recorded as of the Closing Date was a long-term asset of $416.1 million which will be amortized over the life of the contracts as ethylene is received. During 2016, one of the options to obtain additional future ethylene supply at producer economics was exercised by us and, accordingly, additional payments will be made to TDCC of $209.4 million in 2017, which will increase the value of the long-term asset. On February 27, 2017, we exercised the remaining option to obtain additional future ethylene supply and in connection with the exercise we also secured a long-term customer arrangement. Consequently, additional payments will be made to TDCC of between $425.0 million and $465.0 million on or about the fourth quarter of 2020, which will increase the value of the long-term asset.

During 2016, Olin entered into arrangements to increase our supply of low cost electricity. In conjunction with these arrangements, Olin made payments of $175.7 million in 2016. The payments made under these arrangements will be amortized over the life of the contracts as electrical power is received.

The weighted-average useful life of long-term supply contracts at December 31, 2016 was 21 years. For the years ended December 31, 2016 and 2015, amortization expense of $21.5 million and $4.3 million, respectively, was recognized within cost of goods sold related to these supply contracts and is reflected in depreciation and amortization on the consolidated statements of cash flows. We estimate that amortization expense will be approximately $25.0 million in 2017, 2018, 2019, 2020 and 2021 related to these long-term supply contracts. The long-term supply contracts are monitored for impairment each reporting period.