Mid Cap Index Fund Performance Management - Mid Cap Index Fund |
May 31, 2026 |
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| Prospectus [Line Items] | |
| Bar Chart and Performance Table [Heading] | <span style="color:#000000;font-family:Arial;font-size:12pt;font-weight:bold;">Performance Information</span> |
| Performance Narrative [Text Block] | The below bar chart and table illustrate the risks of investing in the Fund by showing changes in the Fund’s performance from calendar year to calendar year and comparing the Fund’s average annual returns to those of the Russell 3000® Index (a broad-based securities market index) and the S&P MidCap 400® Index, which is relevant to the Fund because it has characteristics similar to the Fund’s investment strategies. Fees and expenses incurred at the contract level are not reflected in the bar chart or table. If these amounts were reflected, returns would be less than those shown. Of course, past performance of the Fund is not necessarily an indication of how the Fund will perform in the future.BlackRock Investment Management, LLC (“BlackRock”) assumed sub-advisory responsibilities on April 30, 2025. Prior to this time, the Fund was subadvised by SunAmerica Asset Management, LLC. |
| Performance Past Does Not Indicate Future [Text] | <span style="font-family:Arial;font-size:10pt;">Of course, past </span><span style="font-family:Arial;font-size:10pt;margin-left:0%;">performance of the Fund is not necessarily an indication </span><span style="font-family:Arial;font-size:10pt;">of how the Fund will perform in the future.</span> |
| Performance Information Illustrates Variability of Returns [Text] | <span style="font-family:Arial;font-size:10pt;margin-left:0%;">The below bar chart and table illustrate the risks of investing in the Fund by showing changes in the Fund’s performance from calendar year to calendar year and comparing the Fund’s average annual returns to those of the Russell 3000</span><span style="font-family:Arial;font-size:6.5pt;position:relative;top:-3.25pt;">®</span><span style="font-family:Arial;font-size:10pt;"> Index (a broad-based securities market </span><span style="font-family:Arial;font-size:10pt;margin-left:0%;">index) and the S&P MidCap 400</span><span style="font-family:Arial;font-size:6.5pt;position:relative;top:-3.25pt;">®</span><span style="font-family:Arial;font-size:10pt;"> Index, which is relevant </span><span style="font-family:Arial;font-size:10pt;margin-left:0%;">to the Fund because it has characteristics similar to the Fund’s investment strategies.</span> |
| Bar Chart Does Not Reflect Sales Loads [Text] | <span style="font-family:Arial;font-size:10pt;"> Fees and expenses </span><span style="font-family:Arial;font-size:10pt;margin-left:0%;">incurred at the contract level are not reflected in the bar chart or table. If these amounts were reflected, returns would be less than those shown. </span> |
| Bar Chart Closing [Text Block] | During the period shown in the bar chart:Highest Quarterly Return:December 31, 202024.33%Lowest Quarterly Return:March 31, 2020-29.76%Year to Date Most Recent Quarter:June 30, 202617.20% |
| Performance Table Heading | <span style="font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0%;">Average Annual Total Returns</span><span style="font-family:Arial;font-size:10pt;"> (For the periods ended December 31, 2025)</span> |
| None | |
| Prospectus [Line Items] | |
| Year to Date Return, Label [Optional Text] | <span style="font-family:Arial;font-size:10pt;margin-left:0.0pt;">Year to Date Most </span><span style="font-family:Arial;font-size:10pt;margin-left:0.0pt;">Recent Quarter:</span> |
| Bar Chart, Year to Date Return | 17.20% |
| Bar Chart, Year to Date Return, Date | Jun. 30, 2026 |
| Highest Quarterly Return, Label [Optional Text] | <span style="font-family:Arial;font-size:10pt;margin-left:0.0pt;">Highest Quarterly </span><span style="font-family:Arial;font-size:10pt;margin-left:0.0pt;">Return:</span> |
| Highest Quarterly Return | 24.33% |
| Highest Quarterly Return, Date | Dec. 31, 2020 |
| Lowest Quarterly Return, Label [Optional Text] | <span style="font-family:Arial;font-size:10pt;margin-left:0.0pt;">Lowest Quarterly </span><span style="font-family:Arial;font-size:10pt;margin-left:0.0pt;">Return:</span> |
| Lowest Quarterly Return | (29.76%) |
| Lowest Quarterly Return, Date | Mar. 31, 2020 |