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Retirement Benefits (Unaudited) (Tables)
 3 Months Ended
Mar. 31, 2021
Retirement Benefits [Abstract]  
Components of net periodic benefit cost The cost to the company of its pension and other postretirement benefit (OPB) plans is shown in the following table:
 Three Months Ended March 31
Pension
Benefits		OPB
$ in millions2021202020212020
Components of net periodic benefit cost (benefit)
Service cost$104 $102 $4 $4 
Interest cost263 307 13 17 
Expected return on plan assets(628)(594)(26)(26)
Amortization of prior service (credit) cost(2)(15)— 1 
Net periodic benefit cost (benefit)$(263)$(200)$(9)$(4)
Employer contributions to retirement plans Contributions made by the company to its retirement plans are as follows:
 Three Months Ended March 31
$ in millions20212020
Defined benefit pension plans$27 $20 
OPB plans11 12 
Defined contribution plans266 256