Employee Benefit Plans (Pension Plan and Other Postretirement Benefit Plan Obligations and Plan Assets and Includes a Statement of the Plans Funded Status) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Changes in fair value of plan assets:
Actual return on plan assets		$ 959		$ 743
Employer contributions		40		40		38
Pension Benefits
Changes in benefit obligation:
Service cost		131		116		108
Interest cost		271		268		258
Medicare Part D reimbursement	354
Changes in fair value of plan assets:
Discount rate	4.80%
Other Postretirement Benefits
Changes in benefit obligation:
Service cost		43		44		48
Interest cost		73		79		94
Medicare Part D reimbursement	78
Changes in fair value of plan assets:
Discount rate	4.70%	4.80%
Changes In Benefit Obligation | Pension Benefits
Changes in benefit obligation:
Benefit obligation at beginning of year		6,125		4,981
Service cost		131		116
Interest cost		271		268
Benefits paid		(229)		(208)
Actuarial (gains) losses during the year		(650)		967
Plan amendments		1	[1]	1	[1]
Settlements and curtailments		(24)	[2]	0	[2]
Special termination benefits		0		0
Medicare Part D reimbursement		0		0
Benefit obligation at end of year		5,625		6,125
Changes In Benefit Obligation | Other Postretirement Benefits
Changes in benefit obligation:
Benefit obligation at beginning of year		1,719		1,493
Service cost		43		44
Interest cost		73		79
Benefits paid		(75)		(88)
Actuarial (gains) losses during the year		(170)		191
Plan amendments		(220)	[1]	1	[1]
Settlements and curtailments		(16)	[2]	(6)	[2]
Special termination benefits		1		0
Medicare Part D reimbursement		5		5
Benefit obligation at end of year		1,360		1,719
Changes In Fair Value Of Plan Assets | Pension Benefits
Changes in fair value of plan assets:
Fair value of plan assets at beginning of year		5,553		5,145
Actual return on plan assets		781		611
Employer contributions		8		5
Benefits paid		(229)		(208)
Fair value of plan assets at end of year		6,113		5,553
Funded status at end of year		488		(572)
Changes In Fair Value Of Plan Assets | Other Postretirement Benefits
Changes in fair value of plan assets:
Fair value of plan assets at beginning of year		1,156		1,042
Actual return on plan assets		178		132
Employer contributions		12		16
Benefits paid		(31)		(34)
Fair value of plan assets at end of year		1,315		1,156
Funded status at end of year		(45)		(563)
Level 1 | Pension Benefits
Changes in fair value of plan assets:
Noncurrent pension and other postretirement benefit assets		913		701
Other current liabilities		(15)		(2)
Noncurrent pension and other postretirement benefit liabilities		(410)		(1,271)
Net amount recognized		488		(572)
Level 1 | Other Postretirement Benefits
Changes in fair value of plan assets:
Noncurrent pension and other postretirement benefit assets		29		1
Other current liabilities		(3)		(4)
Noncurrent pension and other postretirement benefit liabilities		(71)		(560)
Net amount recognized		$ (45)		$ (563)
Level 2 | Pension Benefits
Changes in fair value of plan assets:
Discount rate				4.40%	[3]
Weighted average rate of increase for compensation		4.21%		4.21%
Level 2 | Other Postretirement Benefits
Changes in fair value of plan assets:
Discount rate				4.40%	[3]
Weighted average rate of increase for compensation		4.22%		4.22%
Minimum | Level 2 | Pension Benefits
Changes in fair value of plan assets:
Discount rate		5.20%	[3]
Minimum | Level 2 | Other Postretirement Benefits
Changes in fair value of plan assets:
Discount rate		5.00%	[3]
Maximum | Level 2 | Pension Benefits
Changes in fair value of plan assets:
Discount rate		5.30%	[3]
Maximum | Level 2 | Other Postretirement Benefits
Changes in fair value of plan assets:
Discount rate		5.10%	[3]

[1] Relates to a plan amendment that changed medical coverage for certain Medicare-eligible retirees.

[2] 2013 amounts relate primarily to the decommissioning of Kewaunee. 2012 amount relates to the sale of Salem Harbor.

[3] Pension rates are 5.20% for the gas union plans and 5.30% for the nonunion and other union plans. OPEB rates are 5.00% for the gas union plans and 5.10% for the nonunion and other union plans.