Under contract accounting unbillable receivables on long-term contracts arise when the sales or revenues based on performance attainment, though appropriately recognized, cannot be billed yet under terms of the contract as of the balance sheet date.
Any adjustment for the credit quality of unbillable receivables, if required, would be recorded as a direct reduction of revenue.
Factors considered in assessing the collectability of unbillable receivables include, but are not limited to, a customer’s extended delinquency, requests for restructuring and filings for bankruptcy.
Unbillable receivables related to commercial customers expected to be collected after one year were $172 and $172 at December 31, 2017 and 2016.
Accounts receivable related to claims are items that we believe are earned, but are subject to uncertainty concerning their determination or ultimate realization.
Accounts receivable, other than those described above, expected to be collected after one year are not material.
Note 6 – Inventories Inventories at December 31 consisted of the following:
## Table 0 ##
Long-Term Contracts in Progress Long-term contracts in progress includes Delta launch program inventory that is being sold at cost to United Launch Alliance (ULA) under an inventory supply agreement that terminates on March 31, 2021.
The inventory balance was $120 (net of advances of $164 and $220) at December 31, 2017 and 2016.
See indemnifications to ULA in Note 12.
Included in inventories at December 31, 2017 and 2016 are capitalized precontract costs of $933 and $729 primarily related to KC-46A Tanker, C-17 and F/A-18.
See Note 11.
Commercial Aircraft Programs At December 31, 2017 and 2016, commercial aircraft programs inventory included the following amounts related to the 787 program: $30,695 and $32,501 of work in process (including deferred production costs of $25,358 and $27,308), $3,189 and $2,398 of supplier advances, and $3,173 and $3,625 of unamortized tooling and other non-recurring costs.
At December 31, 2017, $22,220 of 787 deferred production costs, unamortized tooling and other non-recurring costs are expected to be recovered from units included in the program accounting quantity that have firm orders and $6,311 is expected to be recovered from units included in the program accounting quantity that represent expected future orders.
At December 31, 2017 and 2016, commercial aircraft programs inventory included $151 and $284 of unamortized tooling costs related to the 747 program.
At December 31, 2017, $146 of 747 unamortized tooling costs are expected to be recovered from units included in the program accounting quantity that have firm orders or commitments.
The program accounting quantity includes one already completed aircraft which is being remarketed.
ITEM 6 – SELECTED FINANCIAL DATA
## Table 1 ##
(a) Includes the impact of RBC Bank (USA), which we acquired on March 2, 2012.
(b) Amounts for prior periods have been updated to reflect the first quarter 2014 adoption of Accounting Standards Update (ASU) 2014-01 related to investments in low income housing tax credits.
(c) Includes results of operations for PNC Global Investment Servicing Inc.  (GIS) through June 30, 2010 and the related after-tax gain on sale.
We sold GIS effective July 1, 2010, resulting in a gain of $639 million, or $328 million after taxes, recognized during the third quarter of 2010.
(d) We redeemed the Series N (TARP) Preferred Stock on February 10, 2010.
In connection with the redemption, we accelerated the accretion of the remaining issuance discount on the Series N Preferred Stock and recorded a corresponding reduction in retained earnings of $250 million in the first quarter of 2010.
This resulted in a noncash reduction in net income attributable to common shareholders and related basic and diluted earnings per share.
The Series N Preferred Stock was issued on December 31, 2008.
Certain prior period amounts have been reclassified to conform with the current period presentation, which we believe is more meaningful to readers of our consolidated financial statements.
This Selected Financial Data should be reviewed in conjunction with the Consolidated Financial Statements and Notes included in Item 8 of this Report as well as the other disclosure in this Report concerning our historical financial performance, our future prospects and the risks associated with our business and financial performance.
The discount rate used to measure pension obligations is determined by comparing the expected future benefits that will be paid under the plan with yields available on high quality corporate bonds of similar duration.
The impact on pension expense of a .5% decrease in discount rate in the current environment is an increase of $18 million per year.
This sensitivity depends on the economic environment and amount of unrecognized actuarial gains or losses on the measurement date.
The expected long-term return on assets assumption also has a significant effect on pension expense.
The expected return on plan assets is a long-term assumption established by considering historical and anticipated returns of the asset classes invested in by the pension plan and the asset allocation policy currently in place.
For purposes of setting and reviewing this assumption, “long term” refers to the period over which the plan’s projected benefit obligations will be disbursed.
We review this assumption at each measurement date and adjust it if warranted.
Our selection process references certain historical data and the current environment, but primarily utilizes qualitative judgment regarding future return expectations.
To evaluate the continued reasonableness of our assumption, we examine a variety of viewpoints and data.
Various studies have shown that portfolios comprised primarily of U. S.  equity securities have historically returned approximately 9% annually over long periods of time, while U. S.  debt securities have returned approximately 6% annually over long periods.
Application of these historical returns to the plan’s allocation ranges for equities and bonds produces a result between 6.50% and 7.25% and is one point of reference, among many other factors, that is taken into consideration.
We also examine the plan’s actual historical returns over various periods and consider the current economic environment.
Recent experience is considered in our evaluation with appropriate consideration that, especially for short time periods, recent returns are not reliable indicators of future returns.
While annual returns can vary significantly (actual returns for 2014, 2013 and 2012 were +6.50%, +15.48%, and +15.29%, respectively), the selected assumption represents our estimated long-term average prospective returns.
Acknowledging the potentially wide range for this assumption, we also annually examine the assumption used by other companies with similar pension investment strategies, so that we can ascertain whether our determinations markedly differ from others.
In all cases, however, this data simply informs our process, which places the greatest emphasis on our qualitative judgment of future investment returns, given the conditions existing at each annual measurement date.
Taking into consideration all of these factors, the expected long-term return on plan assets for determining net periodic pension cost for 2014 was 7.00%, down from 7.50% for 2013.
After considering the views of both internal and external capital market advisors, particularly with regard to the effects of the recent economic environment on long-term prospective fixed income returns, we are reducing our expected long-term return on assets to 6.75% for determining pension cost for 2015.
Under current accounting rules, the difference between expected long-term returns and actual returns is accumulated and amortized to pension expense over future periods.
Each one percentage point difference in actual return compared with our expected return can cause expense in subsequent years to increase or decrease by up to $9 million as the impact is amortized into results of operations.
We currently estimate pretax pension expense of $9 million in 2015 compared with pretax income of $7 million in 2014.
This year-over-year expected increase in expense reflects the effects of the lower expected return on asset assumption, improved mortality, and the lower discount rate required to be used in 2015.
These factors will be partially offset by the favorable impact of the increase in plan assets at December 31, 2014 and the assumed return on a $200 million voluntary contribution to the plan made in February 2015.
The table below reflects the estimated effects on pension expense of certain changes in annual assumptions, using 2015 estimated expense as a baseline.
Table 26: Pension Expense – Sensitivity Analysis
## Table 2 ##
(a) The impact is the effect of changing the specified assumption while holding all other assumptions constant.
Our pension plan contribution requirements are not particularly sensitive to actuarial assumptions.
Investment performance has the most impact on contribution requirements and will drive the amount of required contributions in future years.
Also, current law, including the provisions of the Pension Protection Act of 2006, sets limits as to both minimum and maximum contributions to the plan.
Notwithstanding the voluntary contribution made in February 2015 noted above, we do not expect to be required to make any contributions to the plan during 2015.
We maintain other defined benefit plans that have a less significant effect on financial results, including various nonqualified supplemental retirement plans for certain employees, which are described more fully in Note 13 Employee Benefit Plans in the Notes To Consolidated Financial Statements in Item 8 of this Report.

Tables referenced above, in order (Table 0 first):
<table><tr><td></td><td>2017</td><td>2016</td></tr><tr><td>Long-term contracts in progress</td><td>$13,889</td><td>$12,801</td></tr><tr><td>Commercial aircraft programs</td><td>52,861</td><td>52,048</td></tr><tr><td>Commercial spare parts, used aircraft, general stock materials and other</td><td>5,688</td><td>5,446</td></tr><tr><td>Inventory before advances and progress billings</td><td>72,438</td><td>70,295</td></tr><tr><td>Less advances and progress billings</td><td>-28,094</td><td>-27,096</td></tr><tr><td>Total</td><td>$44,344</td><td>$43,199</td></tr></table>
<table><tr><td></td><td colspan="5">Year ended December 31</td></tr><tr><td>Dollars in millions, except per share data</td><td>2014 (a)</td><td>2013 (a)</td><td>2012 (a)</td><td>2011</td><td>2010</td></tr><tr><td> SUMMARYOFOPERATIONS</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Interest income</td><td>$9,431</td><td>$10,007</td><td>$10,734</td><td>$10,194</td><td>$11,150</td></tr><tr><td>Interest expense</td><td>906</td><td>860</td><td>1,094</td><td>1,494</td><td>1,920</td></tr><tr><td>Net interest income</td><td>8,525</td><td>9,147</td><td>9,640</td><td>8,700</td><td>9,230</td></tr><tr><td>Noninterest income</td><td>6,850</td><td>6,865</td><td>5,872</td><td>5,626</td><td>5,946</td></tr><tr><td>Total revenue</td><td>15,375</td><td>16,012</td><td>15,512</td><td>14,326</td><td>15,176</td></tr><tr><td>Provision for credit losses</td><td>273</td><td>643</td><td>987</td><td>1,152</td><td>2,502</td></tr><tr><td>Noninterest expense (b)</td><td>9,488</td><td>9,681</td><td>10,486</td><td>9,022</td><td>8,529</td></tr><tr><td>Income from continuing operations before income taxes and noncontrolling interests</td><td>5,614</td><td>5,688</td><td>4,039</td><td>4,152</td><td>4,145</td></tr><tr><td>Income taxes (b)</td><td>1,407</td><td>1,476</td><td>1,045</td><td>1,087</td><td>1,127</td></tr><tr><td>Income from continuing operations before noncontrolling interests</td><td>4,207</td><td>4,212</td><td>2,994</td><td>3,065</td><td>3,018</td></tr><tr><td>Income from discontinued operations (net of income taxes of zero, zero, zero, zero and$338) (c)</td><td></td><td></td><td></td><td></td><td>373</td></tr><tr><td>Net income (b)</td><td>4,207</td><td>4,212</td><td>2,994</td><td>3,065</td><td>3,391</td></tr><tr><td>Less: Net income (loss) attributable to noncontrolling interests (b)</td><td>23</td><td>11</td><td>-7</td><td>16</td><td>-11</td></tr><tr><td>Preferred stock dividends (d)</td><td>232</td><td>237</td><td>177</td><td>56</td><td>146</td></tr><tr><td>Preferred stock discount accretion and redemptions (d)</td><td>5</td><td>12</td><td>4</td><td>2</td><td>255</td></tr><tr><td>Net income attributable to common shareholders (d)</td><td>$3,947</td><td>$3,952</td><td>$2,820</td><td>$2,991</td><td>$3,001</td></tr><tr><td> PERCOMMONSHARE</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Basic earnings</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Continuing operations (b)</td><td>$7.44</td><td>$7.45</td><td>$5.33</td><td>$5.69</td><td>$5.06</td></tr><tr><td>Discontinued operations (c)</td><td></td><td></td><td></td><td></td><td>.72</td></tr><tr><td>Net income</td><td>$7.44</td><td>$7.45</td><td>$5.33</td><td>$5.69</td><td>$5.78</td></tr><tr><td>Diluted earnings</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Continuing operations (b)</td><td>$7.30</td><td>$7.36</td><td>$5.28</td><td>$5.62</td><td>$5.00</td></tr><tr><td>Discontinued operations (c)</td><td></td><td></td><td></td><td></td><td>.72</td></tr><tr><td>Net income</td><td>$7.30</td><td>$7.36</td><td>$5.28</td><td>$5.62</td><td>$5.72</td></tr><tr><td>Book value (b)</td><td>$77.61</td><td>$72.07</td><td>$66.95</td><td>$61.44</td><td>$56.22</td></tr><tr><td>Cash dividends declared</td><td>$1.88</td><td>$1.72</td><td>$1.55</td><td>$1.15</td><td>$.40</td></tr></table>
<table><tr><td>Change in Assumption (a)</td><td>EstimatedIncrease/(Decrease)to 2015PensionExpense(In millions)</td></tr><tr><td>.5% decrease in discount rate</td><td>$18</td></tr><tr><td>.5% decrease in expected long-term return on assets</td><td>$22</td></tr><tr><td>.5% increase in compensation rate</td><td>$2</td></tr></table>

Question: Which element occupies the greatest proportion in total amount 2014?
Answer: Total revenue