Postretirement benefits (Components of Net Periodic Benefit Expense (Income)) (Details) (USD $) In Millions, unless otherwise specified	2 Months Ended	3 Months Ended		6 Months Ended
	Dec. 31, 2010	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2012	Apr. 30, 2011
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Cost Recognized	$ 10	$ 14	$ 8	$ 24	$ 18
Pension Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost for benefits earned during the period		4	5	8	9
Interest on obligations		43	47	86	94
Amortization of cumulative loss		27	25	55	50
Amortization of prior service benefit		0	0	0	0
Curtailments		0	0	0	2
Contractual termination benefits		0	0	0	3
Premium on Pension Insurance		1	1	1	1
Expected return on assets		(48)	(53)	(96)	(105)
Net postretirement benefits expense (income)		27	25	54	54
Health and Life Insurance Benefits [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost for benefits earned during the period		2	2	4	4
Interest on obligations		21	14	42	27
Amortization of cumulative loss		11	0	20	0
Amortization of prior service benefit		(1)	(7)	(2)	(15)
Curtailments		0	0	0	0
Contractual termination benefits		0	0	(3)	0
Premium on Pension Insurance		0	0	0	0
Expected return on assets		(9)	(11)	(18)	(21)
Net postretirement benefits expense (income)		$ 24	$ (2)	$ 43	$ (5)