Employee Benefit Plans (AOCI and regulatory assets and liabilities that have not been recognized as components of periodic benefit (credit) cost) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Net actuarial loss	$ (610)		$ (330)
Pension Benefits [Member]
Net actuarial loss	2,211		1,773
Prior service (credit) cost	14		17
Total	2,225	[1]	1,790	[1]
Related expenses	2,200		1,800
Regulatory assets and liabilities			978
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	1,400
Other Postretirement Benefits [Member]
Net actuarial loss	100		268
Prior service (credit) cost	(86)		(28)
Total	14	[1]	240	[1]
Related expenses	14		240
Regulatory assets and liabilities	16		75
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	$ (2)

[1] As of December 31, 2011, of the $2.2 billion related to pension benefits, $1.4 billion is included in AOCI, with the remainder included in regulatory assets and liabilities; the $14 million related to other postretirement benefits consists of $16 million included in regulatory assets and liabilities and $(2) million included in AOCI. As of December 31, 2010, of the $1.8 billion and $240 million related to pension benefits and other postretirement benefits, $978 million and $75 million, respectively, are included in AOCI, with the remainder included in regulatory assets and liabilities.