Pension plans - Additional tabular disclosures (Detail) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assumptions applicable to pension benefit obligations and pension expense:
Discount rate	3.80%	4.10%	3.80%
Expected long-term rate of return on plan assets	6.10%	6.50%	6.70%
Rate of compensation increase	3.00%	3.40%	3.40%
Discount rate applicable to pension expense	4.20%	3.80%	4.60%
Amounts recognized in other comprehensive income:
Accumulated other comprehensive income (loss), beginning of year	$ (1,193)	$ (1,617)
Amount included in net periodic pension expense	101	129
Actuarial gains and other	253	295
Accumulated other comprehensive income (loss), end of year	$ (839)	$ (1,193)	$ (1,617)