Pension Plans and Other Postretirement Benefits - Additional Information (Detail) (USD $) In Millions	9 Months Ended
	Sep. 30, 2011
Pension Plans, Defined Benefit [Member] | Funded Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 269
Expected employer contributions during the remainder of 2011	3
Pension Plans, Defined Benefit [Member] | Unfunded Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	8
Expected employer contributions during the remainder of 2011	21
Other Postretirement Benefit Plans, Defined Benefit [Member] | Unfunded Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	13
Expected employer contributions during the remainder of 2011	$ 5