Pension plans - Additional tabular disclosures (Detail) (Pension Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Amounts recognized in the Consolidated Balance Sheets:
Defined benefit plan, amounts recognized in balance sheet	$ 3,842	$ 2,352
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income
Accumulated other comprehensive income (loss), beginning of year	(1,395)	(1,368)
Amount included in net periodic pension expense	76	53
Gains (losses) current period and other	(1,202)	(80)
Accumulated other comprehensive income (loss), end of year	(2,521)	(1,395)
Assumptions applicable to pension benefit obligations:
Discount rate	4.60%	5.40%
Expected long-term rate of return on plan assets	6.90%	7.10%
Rate of compensation increase	3.70%	3.70%
Discount rate applicable to pension expense	5.30%	5.80%
Accounts Payable, Accruals and Other Liabilities [Member]
Amounts recognized in the Consolidated Balance Sheets:
Accounts payable, accruals and other liabilities - Defined Benefit Pension Plans	3,900	2,425
Other Asset [Member]
Amounts recognized in the Consolidated Balance Sheets:
Other assets - Defined Benefit Pension Plans	$ (58)	$ (73)