Fair Value (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Fair Value Disclosures Details Abstract
An input assumption is considered significant if it affects the fair value by at least 10%.	10.00%		10.00%
Assets [Line Items]
Available-for-sale securities	$ 1,259		$ 1,259		$ 1,762
Trading securities	12		12		10
Derivatives	155		155		124
Total assets	1,426		1,426		1,896
Liabilities [Line Items]
Derivatives	440		440		423
Total liabilities	440		440		423
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	45	(7)
Included in earnings	0	23
Included in other comprehensive income	(4)	(40)
Included in regulatory assets	7	2
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	4	(1)
Transfers of assets (liabilities) into Level 3	(58)	(212)
Transfers of (assets) liabilities out of Level 3	16	12
Balance at end of period	10	(223)	10	(223)
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	6	12
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	40	42	42	42
Settlements	0	0	2	0
Balance at end of period	40	42	40	42
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/losses relating to assets held at the end of the period	0	0	0	0
Fair Value Nonrecurring Measurements Abstract
Asset Impairment Charges	33	1	33	1
Assets Fair Value Disclosure Nonrecurring	33		33
Assets Carrying Amount Disclosure Nonrecurring	66		66
Carrying Amount
Assets
Marketable securities	1,271		1,271		1,772
Derivatives	155		155		124
Total assets	1,426		1,426		1,896
Liabilities
Debt	21,435		21,435		19,551
Derivatives	440		440		423
Total liabilities	21,875		21,875		19,974
Fair Value
Assets
Marketable securities	1,271		1,271		1,772
Derivatives	155		155		124
Total assets	1,426		1,426		1,896
Liabilities
Debt	22,179		22,179		20,137
Derivatives	440		440		423
Total liabilities	22,619		22,619		20,560
Quoted Market Prices in Active Market for Identical Assets (Level 1)
Assets [Line Items]
Available-for-sale securities	2		2		8
Trading securities	12		12		10
Derivatives	0		0		0
Total assets	14		14		18
Quoted Market Prices in Active Market for Identical Assets (Level 1)
Liabilities [Line Items]
Derivatives	0		0		0
Total liabilities	0		0		0
Significant Other Observable Inputs (Level 2)
Assets [Line Items]
Available-for-sale securities	1,217		1,217		1,712
Trading securities	0		0		0
Derivatives	72		72		63
Total assets	1,289		1,289		1,775
Significant Other Observable Inputs (Level 2)
Liabilities [Line Items]
Derivatives	367		367		411
Total liabilities	367		367		411
Significant Unobservable Inputs (Level 3)
Assets [Line Items]
Available-for-sale securities	40		40		42
Trading securities	0		0		0
Derivatives	83		83		61
Total assets	123		123		103
Significant Unobservable Inputs (Level 3)
Liabilities [Line Items]
Derivatives	73		73		12
Total liabilities	73		73		12
Interest Rate Derivatives
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	(7)	(18)
Included in earnings	0	1
Included in other comprehensive income	(12)	(12)
Included in regulatory assets	0	(2)
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	1	2
Transfers of assets (liabilities) into Level 3	(58)	(209)
Transfers of (assets) liabilities out of Level 3	16	12
Balance at end of period	(60)	(226)	(60)	(226)
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	0	(1)
Cross Currency Swaps
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	5	(7)
Included in earnings	(2)	(1)
Included in other comprehensive income	8	(28)
Included in regulatory assets	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	4	2
Transfers of assets (liabilities) into Level 3	0	0
Transfers of (assets) liabilities out of Level 3	0	0
Balance at end of period	15	(34)	15	(34)
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	(2)	(1)
Foreign Currency
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	23	(1)
Included in earnings	18	22
Included in other comprehensive income	0	0
Included in regulatory assets	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	(1)	0
Transfers of assets (liabilities) into Level 3	0	(3)
Transfers of (assets) liabilities out of Level 3	(2)	0
Balance at end of period	38	18	38	18
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	15	20
Commodity & Other
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	24	19
Included in earnings	(16)	1
Included in other comprehensive income	0	0
Included in regulatory assets	7	4
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	(5)
Transfers of assets (liabilities) into Level 3	0	0
Transfers of (assets) liabilities out of Level 3	2	0
Balance at end of period	17	19	17	19
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	$ (7)	$ (6)