Accumulated Benefit Obligations in Excess of Fair Value of Plan Assets (Detail) (Qualified Defined Benefit Pension Plans, USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Qualified Defined Benefit Pension Plans
Plans where ABO was in excess of plan assets
Projected benefit obligation	$ 45,875		$ 40,478
Less: fair value of plan assets	30,597		26,976
Unfunded status of plans	(15,278)	[1]	(13,502)	[1]
Plans where ABO was less than plan assets
Projected benefit obligation	142		138
Less: fair value of plan assets	327		316
Funded status of plans	$ 185	[2]	$ 178	[2]

[1] Represent accrued pension liabilities, which are included on our Balance Sheets.

[2] Represent prepaid pension assets, which are included on our Balance Sheets in other noncurrent assets.