Commitments and Guarantees Unrecorded Unconditional Purchase Obligations (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Capital Additions [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	$ 175
Unrecorded Unconditional Purchase Obligation, Due within One Year	58
Unrecorded Unconditional Purchase Obligation, Due within Two Years	18
Unrecorded Unconditional Purchase Obligation, Due within Three Years	10
Unrecorded Unconditional Purchase Obligation, Due within Four Years	10
Unrecorded Unconditional Purchase Obligation, Due within Five Years	6
Unrecorded Unconditional Purchase Obligation, Due after Five Years	73
Long-term Contract for Purchase of Electric Power [Domain]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	796
Unrecorded Unconditional Purchase Obligation, Due within One Year	129
Unrecorded Unconditional Purchase Obligation, Due within Two Years	77
Unrecorded Unconditional Purchase Obligation, Due within Three Years	76
Unrecorded Unconditional Purchase Obligation, Due within Four Years	76
Unrecorded Unconditional Purchase Obligation, Due within Five Years	57
Unrecorded Unconditional Purchase Obligation, Due after Five Years	381
Electric Transmission [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	102
Unrecorded Unconditional Purchase Obligation, Due within One Year	21
Unrecorded Unconditional Purchase Obligation, Due within Two Years	21
Unrecorded Unconditional Purchase Obligation, Due within Three Years	21
Unrecorded Unconditional Purchase Obligation, Due within Four Years	20
Unrecorded Unconditional Purchase Obligation, Due within Five Years	19
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Public Utility Districts [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	68
Unrecorded Unconditional Purchase Obligation, Due within One Year	7
Unrecorded Unconditional Purchase Obligation, Due within Two Years	8
Unrecorded Unconditional Purchase Obligation, Due within Three Years	8
Unrecorded Unconditional Purchase Obligation, Due within Four Years	8
Unrecorded Unconditional Purchase Obligation, Due within Five Years	7
Unrecorded Unconditional Purchase Obligation, Due after Five Years	30
Public Utilities, Inventory, Fuel [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	136
Unrecorded Unconditional Purchase Obligation, Due within One Year	49
Unrecorded Unconditional Purchase Obligation, Due within Two Years	22
Unrecorded Unconditional Purchase Obligation, Due within Three Years	22
Unrecorded Unconditional Purchase Obligation, Due within Four Years	20
Unrecorded Unconditional Purchase Obligation, Due within Five Years	12
Unrecorded Unconditional Purchase Obligation, Due after Five Years	11
Coal Supply Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	53
Unrecorded Unconditional Purchase Obligation, Due within One Year	25
Unrecorded Unconditional Purchase Obligation, Due within Two Years	19
Unrecorded Unconditional Purchase Obligation, Due within Three Years	9
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
Lease Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	244
Unrecorded Unconditional Purchase Obligation, Due within One Year	9
Unrecorded Unconditional Purchase Obligation, Due within Two Years	10
Unrecorded Unconditional Purchase Obligation, Due within Three Years	9
Unrecorded Unconditional Purchase Obligation, Due within Four Years	10
Unrecorded Unconditional Purchase Obligation, Due within Five Years	10
Unrecorded Unconditional Purchase Obligation, Due after Five Years	196
Commitments [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation	1,574
Unrecorded Unconditional Purchase Obligation, Due within One Year	298
Unrecorded Unconditional Purchase Obligation, Due within Two Years	175
Unrecorded Unconditional Purchase Obligation, Due within Three Years	155
Unrecorded Unconditional Purchase Obligation, Due within Four Years	144
Unrecorded Unconditional Purchase Obligation, Due within Five Years	111
Unrecorded Unconditional Purchase Obligation, Due after Five Years	$ 691