Employee Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Benefits [Member]
Component of periodic benefit cost
Service cost	$ 26	$ 28
Interest cost	63	64
Expected return on plan assets	(78)	(74)
Amortization of prior service credit	(2)	(2)
Amortization of actuarial loss	53	37
Net periodic benefit cost	62	53
Other Postretirement Benefits [Member]
Component of periodic benefit cost
Service cost	1	1
Interest cost	5	5
Expected return on plan assets	(3)	(4)
Amortization of prior service credit	0
Amortization of actuarial loss	0
Net periodic benefit cost	$ 3	$ 2