Intangible assets such as patents, customer-related intangible assets and other intangible assets with finite useful lives are amortized on a straight-line basis over their estimated economic lives.
The weighted-average useful lives approximate the following:
## Table 0 ##
Recoverability of intangible assets with finite useful lives is assessed in the same manner as property, plant and equipment as described above.
Income Taxes: For purposes of the Company’s Consolidated Financial Statements for periods prior to the Spin-off, income tax expense has been recorded as if the Company filed tax returns on a stand-alone basis separate from Ingersoll Rand.
This separate return methodology applies the accounting guidance for income taxes to the stand-alone financial statements as if the Company was a stand-alone enterprise for the periods prior to the Spin-off.
Therefore, cash tax payments and items of current and deferred taxes may not be reflective of the Company’s actual tax balances prior to or subsequent to the Spin-off.
Cash paid for income taxes, net of refunds for the twelve months ended December 31, 2016 and 2015 was $10.4 million and $80.6 million, respectively.
The 2016 net cash income taxes paid includes a refund of $46.2 million received from the Canadian Tax Authorities.
The income tax accounts reflected in the Consolidated Balance Sheet as of December 31, 2016 and 2015 include income taxes payable and deferred taxes allocated to the Company at the time of the Spin-off.
The calculation of the Company’s income taxes involves considerable judgment and the use of both estimates and allocations.
Deferred tax assets and liabilities are determined based on temporary differences between financial reporting and tax bases of assets and liabilities, applying enacted tax rates expected to be in effect for the year in which the differences are expected to reverse.
The Company recognizes future tax benefits, such as net operating losses and tax credits, to the extent that realizing these benefits is considered in its judgment to be more likely than not.
The Company regularly reviews the recoverability of its deferred tax assets considering its historic profitability, projected future taxable income, timing of the reversals of existing temporary differences and the feasibility of its tax planning strategies.
Where appropriate, the Company records a valuation allowance with respect to a future tax benefit.
Product Warranties: Standard product warranty accruals are recorded at the time of sale and are estimated based upon product warranty terms and historical experience.
The Company assesses the adequacy of its liabilities and will make adjustments as necessary based on known or anticipated warranty claims, or as new information becomes available.
Revenue Recognition: Revenue is recognized and earned when all of the following criteria are satisfied: (a) persuasive evidence of a sales arrangement exists; (b) the price is fixed or determinable; (c) collectability is reasonably assured; and (d) delivery has occurred or service has been rendered.
Delivery generally occurs when the title and the risks and rewards of ownership have transferred to the customer.
Both the persuasive evidence of a sales arrangement and fixed or determinable price criteria are deemed to be satisfied upon receipt of an executed and legally binding sales agreement or contract that clearly defines the terms and conditions of the transaction including the respective obligations of the parties.
If the defined terms and conditions allow variability in all or a component of the price, revenue is not recognized until such time that the price becomes fixed or determinable.
At the point of sale, the Company validates the existence of an enforceable claim that requires payment within a reasonable amount of time and assesses the collectability of that claim.
If collectability is not deemed to be reasonably assured, then revenue recognition is deferred until such time that collectability becomes probable or cash is received.
Delivery is not considered to have occurred until the customer has taken title and assumed the risks and rewards of ownership.
Service and installation revenue are recognized when earned.
In some instances, customer acceptance provisions are included in sales arrangements to give the buyer the ability to ensure the delivered product or service meets the criteria established in the order.
In these instances, revenue recognition is deferred until the acceptance terms specified in the arrangement are fulfilled through customer acceptance or a demonstration that established criteria have been satisfied.
If uncertainty exists about customer acceptance, revenue is not recognized until acceptance has occurred.
The Company offers various sales incentive programs to our customers, dealers, and distributors.
Sales incentive programs do not preclude revenue recognition, but do require an accrual for the Company’s best estimate of expected activity.
Examples of the sales incentives that are accrued for as a contra receivable and sales deduction at the point of sale include, but are not limited to, discounts (i. e.  net 30 type), coupons, and rebates where the customer does not have to provide any additional requirements to receive the discount.
Sales returns and customer disputes involving a question of quantity or price are also accounted for as a
CMS ENERGY CORPORATION NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED) high-yield and global bond funds.
Alternative strategies are diversified across absolute return investment approaches and global tactical asset allocation.
We use annual liability measurements, quarterly portfolio reviews, and periodic asset/liability studies to evaluate the need for adjustments to the portfolio allocation.
We established union and non-union VEBA trusts to fund our future retiree health and life insurance benefits.
These trusts are funded through the ratemaking process for Consumers and through direct contributions from the non-utility subsidiaries.
We invest the equity portions of the union and non-union health care VEBA trusts in a Standard & Poor’s 500 Index fund.
We invest the fixed-income portion of the union health care VEBA trust in domestic investment grade taxable instruments.
We invest the fixed-income portion of the non-union health care VEBA trust in a diversified mix of domestic tax-exempt securities.
The investment selections of each VEBA trust are influenced by the tax consequences, as well as the objective of generating asset returns that will meet the medical and life insurance costs of retirees.
SFAS No.132(R) Benefit Payments: The expected benefit payments for each of the next five years and the five-year period thereafter are as follows:
## Table 1 ##
(a) OPEB benefit payments are net of employee contributions and expected Medicare Part D prescription drug subsidy payments.
The subsidies to be received are estimated to be $6 million for 2009 and 2010, $7 million for 2011, $8 million for 2012 and 2013 and $50 million combined for 2014 through 2018.9: ASSET RETIREMENT OBLIGATIONS SFAS No.143, Accounting for Asset Retirement Obligations: This standard requires us to record the fair value of the cost to remove assets at the end of their useful lives, if there is a legal obligation to remove them.
No market risk premium was included in our ARO fair value estimate since a reasonable estimate could not be made.
If a five percent market risk premium were assumed, our ARO liability at December 31, 2008 would increase by $10 million.
If a reasonable estimate of fair value cannot be made in the period in which the ARO is incurred, such as for assets with indeterminate lives, the liability is to be recognized when a reasonable estimate of fair value can be made.
Historically, our gas transmission and electric and gas distribution assets have indeterminate lives and retirement cash flows that cannot be determined.
During 2007, however, we implemented a new fixed asset accounting system that facilitates ARO accounting estimates for gas distribution mains and services.
The new system enabled us to calculate a reasonable estimate of the fair value of the cost to cut, purge, and cap abandoned gas distribution mains and services at the end of their useful lives.
We recorded a $101 million ARO liability and an asset of equal value at December 31, 2007.
We have not recorded a liability for assets that have insignificant cumulative disposal costs, such as substation batteries.
FASB Interpretation No.47, Accounting for Conditional Asset Retirement Obligations: This Interpretation clarified the term “conditional asset retirement obligation” used in SFAS No.143.
The term refers to a legal obligation to perform an asset retirement activity in which the timing or method of settlement are conditional on a future event.
We determined that abatement of asbestos included in our plant investments and the cut, purge, and cap of abandoned gas distribution mains and services qualify as conditional AROs, as defined by FIN 47.
December 31, 2016, Consumers had 86 percent of its 2017 expected coal requirements under contract, as well as a 37-day supply of coal on hand.
In conjunction with its coal supply contracts, Consumers leases a fleet of rail cars and has transportation contracts with various companies to provide rail and vessel services for delivery of purchased coal to Consumers’ generating facilities.
Consumers’ coal transportation contracts expire on various dates from 2017 through 2019; payment obligations under these contracts totaled $259 million at December 31, 2016.
During 2016, 17 percent of the energy Consumers provided to customers was generated by natural gasfueled generating units, which burned 45 bcf of natural gas and produced a combined total of 6,194 GWh of electricity.
In order to obtain the gas it needs for electric generation fuel, Consumers’ electric utility purchases gas from the market near the time of consumption, at prices that allow it to compete in the electric wholesale market.
For units 3 and 4 of D. E.  Karn and for the Jackson and Zeeland plants, Consumers utilizes an agent that owns firm transportation rights to each plant to purchase gas from the market and transport the gas to the facilities.
For its smaller combustion turbines, Consumers’ electric utility purchases and transports gas to its facilities as a bundled-rate tariff customer of either the gas utility or DTE Gas.
Presented in the following table is the cost per million Btu of all fuels consumed, which fluctuates with the mix of fuel used.
## Table 2 ##
Electric Utility Competition: Consumers’ electric utility business is subject to actual and potential competition from many sources, in both the wholesale and retail markets, as well as in electric generation, electric delivery, and retail services.
Under existing Michigan law, electric customers in Consumers’ service territory are allowed to buy electric generation service from alternative electric suppliers in an aggregate amount up to ten percent of Consumers’ weather-adjusted retail sales for the preceding calendar year.
At December 31, 2016, electric deliveries under the ROA program were at the ten-percent limit.
Of Consumers’ 1.8 million electric customers, 305 customers, or 0.02 percent, purchased generation service under the ROA program.
The 2016 Energy Law, which will become effective in April 2017, retains the ten-percent cap on ROA, with certain exceptions.
For additional information see Item 8.
Financial Statements and Supplementary Data—MD&A—Outlook—Consumers Electric Utility Outlook and Uncertainties.
Consumers also faces competition or potential competition associated with industrial customers relocating all or a portion of their production capacity outside of Consumers’ service territory for economic reasons; municipalities owning or operating competing electric delivery systems; and customer self-generation.
Consumers addresses this competition in various ways, including: ?
aggressively controlling operating, maintenance, and fuel costs and passing savings on to customers ?
providing competitive rate-design options, particularly for large energy-intensive customers ?
offering tariff-based incentives that support economic development ?
providing non-energy services and value to customers ?
monitoring activity in adjacent geographical areas
Financing Activities Presented in the following table are specific components of net cash provided by (used in) financing activities for 2017, 2016, and 2015:
## Table 3 ##
For 2017, net cash provided by financing activities at CMS Energy decreased $145 million compared with 2016 and net cash provided by financing activities at Consumers decreased $219 million compared with 2016.
These changes were due primarily to higher repayments under Consumers’ commercial paper program, an increase in debt retirements, and, at CMS Energy, lower issuances of certificates of deposit at EnerBank.
These decreases were offset partially by higher debt issuances and, at Consumers, a higher stockholder contribution from CMS Energy.
For 2016, net cash provided by financing activities at CMS Energy decreased $208 million compared with 2015 and net cash provided by financing activities at Consumers increased $202 million compared with 2015.
At CMS Energy, this change was due primarily to an increase in debt retirements and lower issuances of certificates of deposit at EnerBank, offset partially by higher debt issuances and higher repayments under Consumers’ commercial paper program.
At Consumers, a higher stockholder contribution from CMS Energy and an increase in debt issuances, offset partially by debt retirements, contributed to the increase in net cash provided by financing activities in 2016 at Consumers.

<table><tr><td>Customer relationships</td><td>25</td><td>years</td></tr><tr><td>Trademarks</td><td>25</td><td>years</td></tr><tr><td>Completed technology/patents</td><td>10</td><td>years</td></tr><tr><td>Other</td><td>25</td><td>years</td></tr></table>
<table><tr><td></td><td> Pension</td><td> SERP</td><td> OPEB(a)</td></tr><tr><td></td><td colspan="3"> In Millions</td></tr><tr><td>2009</td><td>$72</td><td>$5</td><td>$57</td></tr><tr><td>2010</td><td>78</td><td>5</td><td>60</td></tr><tr><td>2011</td><td>85</td><td>5</td><td>62</td></tr><tr><td>2012</td><td>96</td><td>6</td><td>64</td></tr><tr><td>2013</td><td>106</td><td>6</td><td>65</td></tr><tr><td>2014-2018</td><td>669</td><td>39</td><td>363</td></tr></table>
<table><tr><td>Years Ended December 31</td><td>2016</td><td>2015</td><td>2014</td><td>2013</td><td>2012</td></tr><tr><td>Coal</td><td>$2.40</td><td>$2.49</td><td>$2.72</td><td>$2.90</td><td>$2.98</td></tr><tr><td>Gas</td><td>2.93</td><td>3.06</td><td>7.19</td><td>4.68</td><td>3.16</td></tr><tr><td>Oil</td><td>9.98</td><td>12.28</td><td>20.16</td><td>19.47</td><td>19.08</td></tr><tr><td>Weighted-average fuel cost</td><td>$2.60</td><td>$2.59</td><td>$3.17</td><td>$3.07</td><td>$3.05</td></tr></table>
<table><tr><td>Years Ended December 31</td><td>2017</td><td>2016</td><td>Change</td><td>2016</td><td>2015</td><td>In Millions Change</td></tr><tr><td> CMS Energy, including Consumers</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Issuance of debt</td><td>$1,633</td><td>$1,049</td><td>$584</td><td>$1,049</td><td>$599</td><td>$450</td></tr><tr><td>Net increase in EnerBank certificates of deposit</td><td>47</td><td>100</td><td>-53</td><td>100</td><td>214</td><td>-114</td></tr><tr><td>Issuance of common stock</td><td>83</td><td>72</td><td>11</td><td>72</td><td>43</td><td>29</td></tr><tr><td>Retirement of debt</td><td>-980</td><td>-728</td><td>-252</td><td>-728</td><td>-224</td><td>-504</td></tr><tr><td>Debt prepayment costs</td><td>-22</td><td>-18</td><td>-4</td><td>-18</td><td>-</td><td>-18</td></tr><tr><td>Payment of dividends on common and preferred stock</td><td>-377</td><td>-347</td><td>-30</td><td>-347</td><td>-322</td><td>-25</td></tr><tr><td>Change in notes payable</td><td>-228</td><td>149</td><td>-377</td><td>149</td><td>189</td><td>-40</td></tr><tr><td>Other financing activities</td><td>-46</td><td>-22</td><td>-24</td><td>-22</td><td>-36</td><td>14</td></tr><tr><td>Net cash provided by financing activities</td><td>$110</td><td>$255</td><td>$-145</td><td>$255</td><td>$463</td><td>$-208</td></tr><tr><td> Consumers</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Issuance of debt</td><td>$834</td><td>$446</td><td>$388</td><td>$446</td><td>$250</td><td>$196</td></tr><tr><td>Stockholder contribution from CMS Energy</td><td>450</td><td>275</td><td>175</td><td>275</td><td>150</td><td>125</td></tr><tr><td>Payment of dividends on common and preferred stock</td><td>-524</td><td>-501</td><td>-23</td><td>-501</td><td>-476</td><td>-25</td></tr><tr><td>Retirement of debt</td><td>-555</td><td>-198</td><td>-357</td><td>-198</td><td>-124</td><td>-74</td></tr><tr><td>Debt prepayment costs</td><td>-4</td><td>-</td><td>-4</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Change in notes payable</td><td>-228</td><td>149</td><td>-377</td><td>149</td><td>189</td><td>-40</td></tr><tr><td>Other financing activities</td><td>-24</td><td>-3</td><td>-21</td><td>-3</td><td>-23</td><td>20</td></tr><tr><td>Net cash provided by (used in) financing activities</td><td>$-51</td><td>$168</td><td>$-219</td><td>$168</td><td>$-34</td><td>$202</td></tr></table>

Question: What's the average of Issuance of debt in 2017 and 2016? (in millions)