Employee Benefit Plans - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Long Term Incentive Deferred Cash Expense	$ 39	$ 40	$ 78	$ 77
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	21		21
Share Based Compensation Arrangement By Share Based Payment Award Options Available For Additional Grant	17		17
Fair value of options granted per share			$ 7.37	$ 7.83
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	5	6	12	15
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year	8		8
Defined Benefit Plan, Contributions by Employer	1		4
Contributed To Postretirement Welfare Plan	1		1
Expected Medicare Subsidy Reimbursement Amount	$ 3		$ 3
Pension Plans, Defined Benefit
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Expected Long Term Return on Assets	7.00%		7.00%
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Expected Long Term Return on Assets	5.00%		5.00%
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	17		17
Share Based Compensation Arrangement By Share Based Payment Award Options Available For Additional Grant	9		9