Employee Retirement Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Benefits [Member]
Net periodic benefit (income) cost [Abstract]
Service cost	$ 16	$ 16
Interest cost	25	25
Expected return on plan assets	(60)	(60)
Amortization of transition obligation	0	0
Amortization of prior service cost (benefit)	1	(1)
Net periodic benefit (income) cost	(18)	(20)
Other Benefits [Member]
Net periodic benefit (income) cost [Abstract]
Service cost	1	2
Interest cost	5	5
Expected return on plan assets	0	(1)
Amortization of transition obligation	1	1
Amortization of prior service cost (benefit)	0	0
Net periodic benefit (income) cost	$ 7	$ 7