Employee Benefit Plans (Net Periodic Benefit Cost) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Benefits [Member]
Service cost	$ 29	$ 27
Interest cost	67	64
Expected return on plan assets	(108)	(110)
Amortization of prior service cost (credit)	1	1
Amortization of net loss	33	24
Net periodic benefit cost	22	6
Other Postretirement Benefits [Member]
Service cost	11	12
Interest cost	20	23
Expected return on plan assets	(21)	(20)
Amortization of prior service cost (credit)	(3)	(3)
Amortization of net loss	2	3
Net periodic benefit cost	$ 9	$ 15