Employee Benefit Plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined contribution benefit plans [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Cost of defined benefit plans	$ 371	$ 322	$ 307
Restoration Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Number of hours of service required to qualify for the plan	1,000 or more hours
Noncontributory and nonqualified plan, benefit expense	20	25	19
Noncontributory and nonqualified plan, accrued benefits liabilities	120	105
Defined benefit pension plans [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefits expense	49	39	33
Accrued benefits liabilities	196	161
Supplemental Executive Retirement Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefits expense	51	33	27
Accrued benefits liabilities	$ 242	$ 237
Subsequent to March 31, 2008 [Member] | Defined contribution benefit plans [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Percentage of employer contribution to match participant contribution in defined contribution plan, net	100.00%
Subsequent to March 31, 2008 [Member] | Defined contribution benefit plans [Member] | Minimum [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Percentage of employer contribution to match participant contribution in defined contribution plan	3.00%
Subsequent to March 31, 2008 [Member] | Defined contribution benefit plans [Member] | Maximum [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Percentage of employer contribution to match participant contribution in defined contribution plan	9.00%