Employee Benefit Plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended		6 Months Ended			3 Months Ended	6 Months Ended	1 Months Ended
	Jun. 30, 2013	Jun. 30, 2013 D	Dec. 31, 2012	Jun. 30, 2013 Pro Rata Share	Jun. 30, 2013 Pro Rata Share Up to 6.9%	Jun. 30, 2013 Pro Rata Share In excess of 6.9%	Jun. 30, 2013 Pension Benefits	Jun. 30, 2013 Pension Benefits	Feb. 28, 2013 Restricted Stock	Feb. 28, 2013 Restricted Stock Units	Feb. 28, 2013 Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employer contribution to tax-qualified defined benefit pension plans	$ 38	$ 79
Defined benefit plan, curtailment loss							(2)	(2)
Defined benefit plan, settlement gain							1	1
Defined benefit plan, discount rate	4.74%	4.74%	4.24%
Reduction of projected benefit obligation of the plans		(434)
Curtailment, settlements and corresponding remeasurements adjustment in other comprehensive income	(442)	(442)
Plan remeasurements decrease against the expected net periodic benefit cost	30	30
Defined benefit plan curtailment effect	84	84
Number of days used to compute performance period average closing price of restricted stock units		20
Share-Based Compensation, award granted									0.5	0.5	1.3
Share-Based Compensation, vesting period									3 years	3 years	3 years
Share-Based Compensation, vesting date											Dec. 31, 2015
Percentage of pre-tax earnings paid for profit sharing plan		15.00%			10.00%	20.00%
Share-based compensation program pre-tax profits excluding special items, profit sharing expense and share-based compensation program expense threshold		$ 10
Pre-tax margin				6.90%