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Employee Benefit Plans - Rollforward of Level 3 Plan Assets (Details) - Pension Plans - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Pension and Other Postretirement Plans    
Balance at beginning of period $ 3,985 $ 3,553
Balance at end of period 3,605 3,985
Level 3    
Pension and Other Postretirement Plans    
Balance at beginning of period 61 53
Realized and unrealized gains 1 5
Purchases, sales and settlements, net 3 3
Balance at end of period $ 65 $ 61