Components of Net Periodic Pension and Postretirement Benefit Costs (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Pension benefits
Components of net periodic cost
Service cost	$ 38	$ 38	$ 76	$ 76
Interest cost	75	80	149	161
Expected return on plan assets	(99)	(92)	(197)	(184)
Amortization of prior service credit	(1)	(1)	(1)	(1)
Amortization of net actuarial loss (gain)	45	39	89	77
Settlement loss	9	8	19	17
Net periodic cost (credit)	67	72	135	146
Postretirement benefits
Components of net periodic cost
Service cost	3	3	6	6
Interest cost	9	9	18	18
Amortization of prior service credit	(5)	(5)	(11)	(11)
Amortization of net actuarial loss (gain)	(5)	(8)	(10)	(15)
Net periodic cost (credit)	$ 2	$ (1)	$ 3	$ (2)