Benefit Plans - Costs of Benefit Plans (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Other pension information
Income tax expense due to patient protection and affordable care act	$ 0	$ 0	$ 0	$ 22
Pension Benefits
Defined benefit plan disclosure
Service cost	13	12	40	36
Interest cost	35	35	105	105
Expected return on plan assets	(45)	(40)	(136)	(119)
Amortization of actuarial loss	16	13	49	38
Other amortization, net	2	2	5	5
Net periodic cost before deferral	21	22	63	65
Other Postretirement Benefits
Defined benefit plan disclosure
Service cost	3	3	8	7
Interest cost	10	13	30	29
Expected return on plan assets	0	(1)	(1)	(3)
Amortization of actuarial loss	3	6	9	6
Other amortization, net	1	1	4	4
Net periodic cost before deferral	$ 17	$ 22	$ 50	$ 43