Pension plans (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Compensation and Retirement Disclosure [Abstract]
Expenses recognized during period under the defined contributions plans	$ 99	$ 96	$ 87
Fair value of plan assets	487	434
Projected benefit obligation	531	508
Accrued pension liability	44	74
Defined pension plan contribution expected for 2013	18
Estimated net actuarial loss expected to be amortized from AOCI	3
Benefit payments made during period	37	21
Benefit payments for settlement of a defined benefit plan	$ 12