Commitments and Guarantees Unrecorded Unconditional Purchase Obligations (Details) $ in Millions	Dec. 31, 2020 USD ($)
Capital Addition Purchase Commitments [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	$ 347
Unrecorded Unconditional Purchase Obligation, Due within One Year	237
Unrecorded Unconditional Purchase Obligation, Due within Two Years	33
Unrecorded Unconditional Purchase Obligation, Due within Three Years	20
Unrecorded Unconditional Purchase Obligation, Due within Four Years	1
Unrecorded Unconditional Purchase Obligation, Due within Five Years	1
Unrecorded Unconditional Purchase Obligation, Due after Five Years	55
Long-term Contract for Purchase of Electric Power [Domain]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	4,204
Unrecorded Unconditional Purchase Obligation, Due within One Year	250
Unrecorded Unconditional Purchase Obligation, Due within Two Years	257
Unrecorded Unconditional Purchase Obligation, Due within Three Years	284
Unrecorded Unconditional Purchase Obligation, Due within Four Years	278
Unrecorded Unconditional Purchase Obligation, Due within Five Years	249
Unrecorded Unconditional Purchase Obligation, Due after Five Years	2,886
Electric Transmission [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	45
Unrecorded Unconditional Purchase Obligation, Due within One Year	9
Unrecorded Unconditional Purchase Obligation, Due within Two Years	9
Unrecorded Unconditional Purchase Obligation, Due within Three Years	9
Unrecorded Unconditional Purchase Obligation, Due within Four Years	9
Unrecorded Unconditional Purchase Obligation, Due within Five Years	9
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Public Utility Districts [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	131
Unrecorded Unconditional Purchase Obligation, Due within One Year	21
Unrecorded Unconditional Purchase Obligation, Due within Two Years	19
Unrecorded Unconditional Purchase Obligation, Due within Three Years	18
Unrecorded Unconditional Purchase Obligation, Due within Four Years	17
Unrecorded Unconditional Purchase Obligation, Due within Five Years	17
Unrecorded Unconditional Purchase Obligation, Due after Five Years	39
Natural gas [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	800
Unrecorded Unconditional Purchase Obligation, Due within One Year	57
Unrecorded Unconditional Purchase Obligation, Due within Two Years	42
Unrecorded Unconditional Purchase Obligation, Due within Three Years	37
Unrecorded Unconditional Purchase Obligation, Due within Four Years	43
Unrecorded Unconditional Purchase Obligation, Due within Five Years	43
Unrecorded Unconditional Purchase Obligation, Due after Five Years	578
Coal and transportationSupply Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	135
Unrecorded Unconditional Purchase Obligation, Due within One Year	27
Unrecorded Unconditional Purchase Obligation, Due within Two Years	27
Unrecorded Unconditional Purchase Obligation, Due within Three Years	27
Unrecorded Unconditional Purchase Obligation, Due within Four Years	27
Unrecorded Unconditional Purchase Obligation, Due within Five Years	27
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Commitments [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	5,662
Unrecorded Unconditional Purchase Obligation, Due within One Year	601
Unrecorded Unconditional Purchase Obligation, Due within Two Years	387
Unrecorded Unconditional Purchase Obligation, Due within Three Years	395
Unrecorded Unconditional Purchase Obligation, Due within Four Years	375
Unrecorded Unconditional Purchase Obligation, Due within Five Years	346
Unrecorded Unconditional Purchase Obligation, Due after Five Years	$ 3,558