Commitments and Guarantees Unrecorded Unconditional Purchase Obligations (Details) $ in Millions	Dec. 31, 2018 USD ($)
Capital Addition Purchase Commitments [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	$ 213
Unrecorded Unconditional Purchase Obligation, Due within One Year	143
Unrecorded Unconditional Purchase Obligation, Due within Two Years	9
Unrecorded Unconditional Purchase Obligation, Due within Three Years	1
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	58
Long-term Contract for Purchase of Electric Power [Domain]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	2,783
Unrecorded Unconditional Purchase Obligation, Due within One Year	167
Unrecorded Unconditional Purchase Obligation, Due within Two Years	190
Unrecorded Unconditional Purchase Obligation, Due within Three Years	186
Unrecorded Unconditional Purchase Obligation, Due within Four Years	194
Unrecorded Unconditional Purchase Obligation, Due within Five Years	193
Unrecorded Unconditional Purchase Obligation, Due after Five Years	1,853
Electric Transmission [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	46
Unrecorded Unconditional Purchase Obligation, Due within One Year	1
Unrecorded Unconditional Purchase Obligation, Due within Two Years	0
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	18
Public Utility Districts [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	83
Unrecorded Unconditional Purchase Obligation, Due within One Year	12
Unrecorded Unconditional Purchase Obligation, Due within Two Years	11
Unrecorded Unconditional Purchase Obligation, Due within Three Years	9
Unrecorded Unconditional Purchase Obligation, Due within Four Years	8
Unrecorded Unconditional Purchase Obligation, Due within Five Years	8
Unrecorded Unconditional Purchase Obligation, Due after Five Years	35
Natural gas [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	396
Unrecorded Unconditional Purchase Obligation, Due within One Year	54
Unrecorded Unconditional Purchase Obligation, Due within Two Years	42
Unrecorded Unconditional Purchase Obligation, Due within Three Years	31
Unrecorded Unconditional Purchase Obligation, Due within Four Years	31
Unrecorded Unconditional Purchase Obligation, Due within Five Years	30
Unrecorded Unconditional Purchase Obligation, Due after Five Years	208
Coal and transportationSupply Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	6
Unrecorded Unconditional Purchase Obligation, Due within One Year	6
Unrecorded Unconditional Purchase Obligation, Due within Two Years	0
Unrecorded Unconditional Purchase Obligation, Due within Three Years	0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Commitments [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	3,527
Unrecorded Unconditional Purchase Obligation, Due within One Year	383
Unrecorded Unconditional Purchase Obligation, Due within Two Years	252
Unrecorded Unconditional Purchase Obligation, Due within Three Years	236
Unrecorded Unconditional Purchase Obligation, Due within Four Years	243
Unrecorded Unconditional Purchase Obligation, Due within Five Years	241
Unrecorded Unconditional Purchase Obligation, Due after Five Years	$ 2,172