Employee Benefit Plans (Net Periodic Benefit Cost) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Pension Benefits
Service cost	$ 34		$ 29		$ 69		$ 58
Interest cost	67		67		133		134
Expected return on plan assets	(115)		(107)		(229)		(215)
Amortization of prior service cost (credit)	1		1		2		2
Amortization of net loss	44		33		90		66
Settlements and curtailments	(2)	[1]	0	[1]	(2)	[1]	0	[1]
Net periodic benefit cost (credit)	29		23		63		45
Other Postretirement Benefits
Service cost	12		11		24		22
Interest cost	18		20		37		40
Expected return on plan assets	(22)		(20)		(44)		(41)
Amortization of prior service cost (credit)	(3)		(3)		(6)		(6)
Amortization of net loss	2		1		4		3
Settlements and curtailments	(15)	[1]	0	[1]	(15)	[1]	0	[1]
Net periodic benefit cost (credit)	$ (8)		$ 9		$ 0		$ 18

[1] Relate primarily to the decommissioning of Kewaunee.