Employee Benefit Plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended			9 Months Ended			3 Months Ended		9 Months Ended	1 Months Ended
	Sep. 30, 2013	Sep. 30, 2013 D	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Pro Rata Share Pilots	Sep. 30, 2013 Pro Rata Share Pilots Up to 6.9%	Sep. 30, 2013 Pro Rata Share Pilots In excess of 6.9%	Sep. 30, 2013 Pension Benefits	Jun. 30, 2013 Pension Benefits	Sep. 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	$ 122	$ 201
Defined benefit plan, curtailment loss									(2)	(2)
Defined benefit plan, settlement gain	1							1	1	2
Defined benefit plan, discount rate	5.13%	5.13%	4.59%	4.20%
Increase/ decrease in projected benefit obligation of the plans		522
Change in other comprehensive loss due to actuarial gain	41	483
Plan remeasurements decrease against the expected net periodic benefit cost	(13)	(13)
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%