Employee Benefit Plans (Net Periodic Benefit (Credit) Cost and Amounts Recognized in Other Comprehensive Income and Regulatory Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	$ (554)		$ (509)
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities:
Settlements and curtailments	220
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	131		116		108
Interest cost	271		268		258
Expected return on plan assets	(462)		(430)		(440)
Amortization of prior service (credit) cost	3		3		3
Amortization of net actuarial loss	165		132		96
Settlements and curtailments	(2)	[1]	0	[1]	0	[1]
Special termination benefits	0		0		0
Net periodic benefit cost	106		89		25
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities:
Current year net actuarial (gain) loss	(968)		786		534
Prior service (credit) cost	1		0		0
Settlements and curtailments	(22)	[1]	0	[1]	0	[1]
Amortization of net actuarial loss	165		132		96
Amortization of prior service credit (cost)	(3)		(3)		(3)
Total recognized in other comprehensive income and regulatory assets and liabilities	(1,157)		651		435
Significant assumptions used to determine periodic cost:
Discount rate			5.50%		5.90%
Expected long-term rate of return on plan assets	8.50%		8.50%		8.50%
Weighted average rate of increase for compensation	4.21%		4.21%		4.61%
Other Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	43		44		48
Interest cost	73		79		94
Expected return on plan assets	(92)		(79)		(79)
Amortization of prior service (credit) cost	(15)		(13)		(13)
Amortization of net actuarial loss	7		6		12
Settlements and curtailments	(15)	[1]	(4)	[1]	1	[1]
Special termination benefits	(1)				0
Net periodic benefit cost	2		33		63
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities:
Current year net actuarial (gain) loss	(255)		139		(157)
Prior service (credit) cost	(215)		1		(70)
Settlements and curtailments	(7)	[1]	(2)	[1]	(1)	[1]
Amortization of net actuarial loss	7		6		12
Amortization of prior service credit (cost)	15		13		13
Total recognized in other comprehensive income and regulatory assets and liabilities	$ (469)		$ 145		$ (227)
Significant assumptions used to determine periodic cost:
Discount rate			5.50%		5.90%
Expected long-term rate of return on plan assets	7.75%		7.75%		7.75%
Weighted average rate of increase for compensation	4.22%		4.22%		4.62%
Healthcare cost trend rate	7.00%	[2]	7.00%	[2]	7.00%	[2]
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	4.60%	[2]	4.60%	[2]	4.60%	[2]
Year that the rate reaches the ultimate trend rate	2062	[2]	2061	[2]	2060	[2]
Minimum | Pension Benefits
Significant assumptions used to determine periodic cost:
Discount rate	4.40%
Minimum | Other Postretirement Plans
Significant assumptions used to determine periodic cost:
Discount rate	4.40%
Maximum | Pension Benefits
Significant assumptions used to determine periodic cost:
Discount rate	4.80%
Maximum | Other Postretirement Plans
Significant assumptions used to determine periodic cost:
Discount rate	4.80%

[1] 2013 amount relates primarily to the decommissioning of Kewaunee. 2012 amount relates to the sale of Salem Harbor.

[2] Assumptions used to determine periodic cost for the following year.