Purchase Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Capacity [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	$ 2,340
Unrecorded Unconditional Purchase Obligation, Due within Two Years	2,420
Unrecorded Unconditional Purchase Obligation, Due within Three Years	2,430
Unrecorded Unconditional Purchase Obligation, Due within Four Years	2,400
Unrecorded Unconditional Purchase Obligation, Due within Five Years	2,100
Unrecorded Unconditional Purchase Obligation, Due after Five Years	5,700
Unrecorded Unconditional Purchase Obligation	17,390
Capital Additions [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	215
Unrecorded Unconditional Purchase Obligation, Due within Two Years	530
Unrecorded Unconditional Purchase Obligation, Due within Three Years	745
Unrecorded Unconditional Purchase Obligation, Due within Four Years	760
Unrecorded Unconditional Purchase Obligation, Due within Five Years	760
Unrecorded Unconditional Purchase Obligation, Due after Five Years	3,810
Unrecorded Unconditional Purchase Obligation	$ 6,820