Pension and Other Postretirement Benefits - Schedule of Fair Value of Pension and Postretirement Plans' Assets (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Net payable which represents securities purchased not yet settled less interest and dividends earned on various investments	$ 20
Level 1 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Common stock related to plan contribution	$ 36