v3.26.1
Shareholder Report
 6 Months Ended
Jun. 30, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name Capital Group Completion Fund Series
Entity Central Index Key 0002020645
Entity Investment Company Type N-1A
Document Period End Date Jun. 30, 2026
Capital Group Core Bond Completion Fund - Class M  
Shareholder Report [Line Items]  
Fund Name Capital Group Core Bond Completion Fund
Class Name Class M
Trading Symbol CBCFX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Capital Group Core Bond Completion Fund (the "fund") for the period from January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at capitalgroup.com/CGCBCF-M. You can also request this information by contacting us at (800) 421-4225.
Additional Information Phone Number (800) 421-4225
Additional Information Website capitalgroup.com/CGCBCF-M
Expenses [Text Block]
What were the fund costs for the last six months?
(based on a hypothetical $10,000 investment)
Share class
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Class M
$
0
1
0.00
%
2,3
1
Amount less than $1.
2
Amount less than 0.01%
3
Annualized.
Expenses Paid, Amount $ 0 [1]
Expense Ratio, Percent 0.00% [2],[3]
Net Assets $ 40,000,000
Holdings Count | Holding 471
Investment Company, Portfolio Turnover 327.00%
Additional Fund Statistics [Text Block]
Key fund statistics
Fund net assets (in millions)
$
40
Total number of portfolio holdings471
Portfolio turnover rate including
mortgage dollar roll transactions		327
%
Portfolio turnover rate excluding mortgage dollar roll transactions60
%
Holdings [Text Block]
Portfolio holdings by asset type
 (percent of net assets)
Bonds, notes & other debt instruments:
Corporate bonds and notes62.15
%
Mortgage-backed obligations16.83
%
Asset-backed obligations13.53
%
U.S. Treasury bonds & notes5.87
%
Bonds & notes of governments & government agencies outside the U.S.3.84
%
Municipals0.45
%
TBA sale commitments:
Mortgage-backed obligations(13.16
)
%
Short term securities & other assets less
liabilities
*
10.49
%
Total100.00
%
*Includes derivatives.
Capital Group Core Plus Completion Fund - Class M  
Shareholder Report [Line Items]  
Fund Name Capital Group Core Plus Completion Fund
Class Name Class M
Trading Symbol CPCPX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Capital Group Core Plus Completion Fund (the "fund") for the period from January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at capitalgroup.com/CPLUCF-M. You can also request this information by contacting us at (800) 421-4225.
Additional Information Phone Number (800) 421-4225
Additional Information Website capitalgroup.com/CPLUCF-M
Expenses [Text Block]
What were the fund costs for the last six months?
(based on a hypothetical $10,000 investment)
Share class
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Class M
$
0
1
0.00
%
2,3
1
Amount less than $1.
2
Amount less than 0.01%
3
Annualized.
Expenses Paid, Amount $ 0 [1]
Expense Ratio, Percent 0.00% [2],[3]
Net Assets $ 34,000,000
Holdings Count | Holding 418
Investment Company, Portfolio Turnover 352.00%
Additional Fund Statistics [Text Block]
Key fund statistics
Fund net assets (in millions)
$
34
Total number of portfolio holdings418
Portfolio turnover rate including
mortgage dollar roll transactions		352
%
Portfolio turnover rate excluding mortgage dollar roll transactions46
%
Holdings [Text Block]
Portfolio holdings by asset type
 (percent of net assets)
Bonds, notes & other debt instruments:
Corporate bonds and notes54.00
%
Mortgage-backed obligations28.20
%
Asset-backed obligations19.78
%
Bonds & notes of governments & government agencies outside the U.S.6.44
%
Loans1.28
%
U.S. Treasury bonds & notes0.82
%
Equities:
Common stocks0.21
%
Convertible securities:
Convertible bonds & notes0.10
%
Convertible stocks0.06
%
TBA sale commitments:
Mortgage-backed obligations(13.86
)
%
Short term securities & other assets less liabilities2.97
*
%
Total100.00
%
*Includes derivatives.
Capital Group Municipal Income Completion Fund - Class M  
Shareholder Report [Line Items]  
Fund Name Capital Group Municipal Income Completion Fund
Class Name Class M
Trading Symbol MICOX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Capital Group Municipal Income Completion Fund (the "fund") for the period from January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at capitalgroup.com/CGMICF-M. You can also request this information by contacting us at (800) 421-4225.
Additional Information Phone Number (800) 421-4225
Additional Information Website capitalgroup.com/CGMICF-M
Expenses [Text Block]
What were the fund costs for the last six months?
(based on a hypothetical $10,000 investment)
Share class
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Class M
$
0
1
0.00
%
2,3
1
Amount less than $1.
2
Amount less than 0.01%
3
Annualized.
Expenses Paid, Amount $ 0 [1]
Expense Ratio, Percent 0.00% [2],[3]
Net Assets $ 30,000,000
Holdings Count | Holding 80
Investment Company, Portfolio Turnover 12.00%
Additional Fund Statistics [Text Block]
Key fund statistics
Fund net assets (in millions)
$
30
Total number of portfolio holdings80
Portfolio turnover rate12
%
Holdings [Text Block]
Portfolio quality summary
*
(percent of net assets)
Graphical Representation - Allocation 1 Chart
*
Bond ratings, which typically range from AAA/Aaa (highest) to D (lowest), are assigned by credit rating agencies such as Standard & Poor’s, Moody’s and/or Fitch as an indication of an issuer’s creditworthiness. In assigning a credit rating to a security, the fund looks specifically to the ratings assigned to the issuer of the security by Standard & Poor’s, Moody’s and/or Fitch. If agency ratings differ, the security will be considered to have received the highest of those ratings, consistent with the fund’s investment policies. Securities in the “unrated“ category (above) have not been rated by a rating agency; however, the investment adviser performs its own credit analysis and assigns comparable ratings that are used for compliance with the fund’s investment policies.
†
Includes derivatives
[1] Amount less than $1.
[2] Amount less than 0.01%
[3] Annualized.