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Nuclear Decommissioning Trust Fund - Summary of proceeds from sales of available-for-sale securities and related gains and losses (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Regulated Operations [Abstract]    
Realized gains $ 2 $ 3
Realized losses (5) (2)
Proceeds from sale of securities $ 112 $ 113