Employee Benefits (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 Plans [Member]
Components of net periodic benefit cost
Service cost	$ 32	$ 29	$ 64	$ 59
Interest cost	42	42	84	84
Actuarial loss (gain) amortization	40	32	80	63
Expected return on plan assets	(47)	(51)	(95)	(103)
Prior service (credit) cost and transition (asset) obligation amortization	(1)	(3)	(2)	(5)
Net periodic benefit cost	66	49	131	98
Postretirement Welfare Plan [Member]
Components of net periodic benefit cost
Service cost	1	1	2	2
Interest cost	2	2	4	4
Actuarial loss (gain) amortization	(2)	(2)	(4)	(3)
Expected return on plan assets	(1)	(1)	(1)	(2)
Prior service (credit) cost and transition (asset) obligation amortization	0
Net periodic benefit cost			$ 1	$ 1