Employee Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension
Components of net periodic benefit cost
Service cost	$ 22	$ 8
Interest cost	156	59
Expected return on plan assets	(212)	(73)
Recognition of prior service cost	1	1
Recognition of actuarial loss	8	4
Net periodic pension benefit expense	(25)	(1)
Other Post-Retirement Benefits
Components of net periodic benefit cost
Service cost	6	3
Interest cost	43	8
Expected return on plan assets	(11)	(1)
Recognition of prior service cost		(1)
Net periodic pension benefit expense	$ 38	$ 9