Commitments and Contingencies (Wildfire loss accrual) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
2017/2018 Wildfire/Mudslide Events
Loss Contingency Accrual [Roll Forward]
Beginning balance	$ 4,383
Amounts paid	(620)
Ending balance	3,763	$ 4,383
2017/2018 Wildfire/Mudslide Events | Other current liabilities
Loss Contingency Accrual [Roll Forward]
Beginning balance	2,231
Ending balance	1,812	2,231
2017/2018 Wildfire/Mudslide Events | Other long-term liabilities
Loss Contingency Accrual [Roll Forward]
Beginning balance	2,281
Fixed payments to be made under settlement agreements	2,082
Ending balance		2,281
November 2018 - Woolsey Wildfires
Loss Contingency Accrual [Roll Forward]
Litigation settlement		2,212
November 2018 - Woolsey Wildfires | Other current liabilities
Loss Contingency Accrual [Roll Forward]
Ending balance	1,772
November 2018 - Woolsey Wildfires | Other long-term liabilities
Loss Contingency Accrual [Roll Forward]
Beginning balance	2,152
Ending balance	1,951	2,152
Other Wildfire Related Claims
Loss Contingency Accrual [Roll Forward]
Litigation settlement		19
Other Wildfire Related Claims | Other current liabilities
Loss Contingency Accrual [Roll Forward]
Ending balance	40
Other Wildfire Related Claims | Other long-term liabilities
Loss Contingency Accrual [Roll Forward]
Beginning balance	129
Ending balance	$ 131	$ 129