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Pension and Other Postretirement Benefits (Change in Fair Value of Level 3 Assets) (Details) - USD ($)
$ in Millions
12 Months Ended
Apr. 30, 2022
Apr. 30, 2021
Change in fair value of Level 3 Assets    
Beginning balance $ 836  
Ending balance 741 $ 836
Level 3 [Member]    
Change in fair value of Level 3 Assets    
Beginning balance 2 2
Return on assets held at end of year 0 1
Sales and settlements 0 (1)
Ending balance $ 2 $ 2