Employee Benefits - Additional Information (Detail) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Jun. 30, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Pension remeasurement credit (charges)	$ 237,000,000	$ 237,000,000
Discount rate basis point increase		75
Discount rate	5.00%	5.00%	4.20%
Expected return on plan assets			7.50%
Actual return on assets		7.20%
Amount paid in severance benefits over the period	100,000,000	200,000,000
Post employment benefits liability	800,000,000	800,000,000
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan contributions by employer	300,000,000	700,000,000
Pension Remeasurement Gain Primarily Driven By Increase In Discount Rate Assumption
Defined Benefit Plan Disclosure [Line Items]
Pension remeasurement credit (charges)		300,000,000
Pension Charges Driven By Difference Between Expected Return on Assets and Annualized Actual Return On Assets And Other
Defined Benefit Plan Disclosure [Line Items]
Pension remeasurement credit (charges)		$ (100,000,000)