Defined Benefits (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended
	Apr. 30, 2012	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Pension Benefits - U.S. [Member]
Net Periodic Defined Benefit Costs (Credits) [Line Items]
Service cost		$ 26	$ 24
Interest cost		56	55
Expected return on plan assets		(66)	(62)
Amortization of:
Transition obligation		0	0
Prior service cost		6	6
Actuarial (gain) loss		10	6
Net periodic defined benefit costs (credits)		32	29
Pension Benefits - U.K. [Member]
Net Periodic Defined Benefit Costs (Credits) [Line Items]
Service cost		13	5
Interest cost		84	39
Expected return on plan assets		(111)	(52)
Amortization of:
Transition obligation		0	0
Prior service cost		1	1
Actuarial (gain) loss		20	14
Net periodic defined benefit costs (credits)		7	7
Expected contribution to pension plans		307		161
Employer contributions	186
Other Postretirement Benefits - U.S. [Member]
Net Periodic Defined Benefit Costs (Credits) [Line Items]
Service cost		3	3
Interest cost		8	8
Expected return on plan assets		(6)	(6)
Amortization of:
Transition obligation		1	0
Prior service cost		0	0
Actuarial (gain) loss		1	2
Net periodic defined benefit costs (credits)		$ 7	$ 7