Benefit Plans - Costs of Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Pension Benefits
Defined benefit plan disclosure
Service cost	$ 16		$ 13
Interest cost	33		35
Expected return on plan assets	(46)		(45)
Amortization of actuarial loss	23	[1]	14	[1]
Other amortization, net	2	[1]	2	[1]
Net periodic cost	28		19
Other Postretirement Benefits
Defined benefit plan disclosure
Service cost	3		3
Interest cost	10		10
Expected return on plan assets	0		0
Amortization of actuarial loss	6	[1]	3	[1]
Other amortization, net	1	[1]	1	[1]
Net periodic cost	$ 20		$ 17

[1] Adjusted to reflect PEF’s rate treatment. See Note 17B in the 2011 Form 10-K.