Risk Management and Trading Activities (Details 2) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Assets
Collateral and counterparty netting	$ (288)	$ (507)
Total derivative contracts (Assets)	1,183	1,463
Other assets measured at fair value on a recurring basis	65	72
Total assets	1,248	1,535
Liabilities
Collateral and counterparty netting	167	328
Total derivative contracts (Liabilities)	(2,321)	(2,707)
Other liabilities measured at fair value on a recurring basis	0	0
Total liabilities	(2,321)	(2,707)
Commodity [Member]
Assets
Total derivative contracts (Assets)	1,450	1,952
Liabilities
Total derivative contracts (Liabilities)	(2,443)	(3,013)
Commodity [Member] | Level 1 [Member]
Assets
Total derivative contracts (Assets)	224	65
Liabilities
Total derivative contracts (Liabilities)	(121)	(324)
Commodity [Member] | Level 2 [Member]
Assets
Total derivative contracts (Assets)	627	1,308
Liabilities
Total derivative contracts (Liabilities)	(2,095)	(2,519)
Commodity [Member] | Level 3 [Member]
Assets
Total derivative contracts (Assets)	796	883
Liabilities
Total derivative contracts (Liabilities)	(424)	(474)
Commodity [Member] | Collateral and counterparty netting elimination [Member]
Assets
Total derivative contracts (Assets)	(197)	(304)
Liabilities
Total derivative contracts (Liabilities)	197	304
Foreign Exchange [Member]
Assets
Total derivative contracts (Assets)	0	1
Liabilities
Total derivative contracts (Liabilities)	(32)	(12)
Foreign Exchange [Member] | Level 1 [Member]
Assets
Total derivative contracts (Assets)	0	0
Liabilities
Total derivative contracts (Liabilities)	0	0
Foreign Exchange [Member] | Level 2 [Member]
Assets
Total derivative contracts (Assets)	0	1
Liabilities
Total derivative contracts (Liabilities)	(32)	(12)
Foreign Exchange [Member] | Level 3 [Member]
Assets
Total derivative contracts (Assets)	0	0
Liabilities
Total derivative contracts (Liabilities)	0	0
Foreign Exchange [Member] | Collateral and counterparty netting elimination [Member]
Assets
Total derivative contracts (Assets)	0	0
Liabilities
Total derivative contracts (Liabilities)	0	0
Other [Member]
Assets
Total derivative contracts (Assets)	21	17
Liabilities
Total derivative contracts (Liabilities)	(13)	(10)
Other [Member] | Level 1 [Member]
Assets
Total derivative contracts (Assets)	0	0
Liabilities
Total derivative contracts (Liabilities)	0	0
Other [Member] | Level 2 [Member]
Assets
Total derivative contracts (Assets)	21	17
Liabilities
Total derivative contracts (Liabilities)	(13)	(10)
Other [Member] | Level 3 [Member]
Assets
Total derivative contracts (Assets)	1	0
Liabilities
Total derivative contracts (Liabilities)	(1)	0
Other [Member] | Collateral and counterparty netting elimination [Member]
Assets
Total derivative contracts (Assets)	(1)	0
Liabilities
Total derivative contracts (Liabilities)	1	0
Level 1 [Member]
Assets
Collateral and counterparty netting	(31)	(1)
Total derivative contracts (Assets)	193	64
Other assets measured at fair value on a recurring basis	12	20
Total assets	205	84
Liabilities
Collateral and counterparty netting	31	1
Total derivative contracts (Liabilities)	(90)	(323)
Other liabilities measured at fair value on a recurring basis	0	0
Total liabilities	(90)	(323)
Level 2 [Member]
Assets
Collateral and counterparty netting	(88)	(274)
Total derivative contracts (Assets)	560	1,052
Other assets measured at fair value on a recurring basis	53	49
Total assets	613	1,101
Liabilities
Collateral and counterparty netting	88	274
Total derivative contracts (Liabilities)	(2,052)	(2,267)
Other liabilities measured at fair value on a recurring basis	0	0
Total liabilities	(2,052)	(2,267)
Level 3 [Member]
Assets
Collateral and counterparty netting	(6)	(19)
Total derivative contracts (Assets)	791	864
Other assets measured at fair value on a recurring basis	0	3
Total assets	791	867
Liabilities
Collateral and counterparty netting	6	19
Total derivative contracts (Liabilities)	(419)	(455)
Other liabilities measured at fair value on a recurring basis	0	0
Total liabilities	(419)	(455)
Collateral and counterparty netting elimination [Member]
Assets
Collateral and counterparty netting	(163)	(213)
Total derivative contracts (Assets)	(361)	(517)
Other assets measured at fair value on a recurring basis	0	0
Total assets	(361)	(517)
Liabilities
Collateral and counterparty netting	42	34
Total derivative contracts (Liabilities)	240	338
Other liabilities measured at fair value on a recurring basis	0	0
Total liabilities	$ 240	$ 338