Pension plans - Defined benefit pension plans - Narrative (Detail) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation for unfunded plans	$ 1,200	$ 1,200
Amounts recognized in the Consolidated Balance Sheets:
Funded status reflected in liabilities	2,997	2,884
Estimated future benefit payments
2017	992
2018	1,007
2019	987
2020	1,003
2021	994
2022 - 2026	5,043
Expected contribution to pension plans during the next year	224
Other Assets [Member]
Amounts recognized in the Consolidated Balance Sheets:
Funded status reflected in assets	$ 644	$ 456