Expected Future Benefit Payments for Qualified Plan and SERP (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Schedule of Pension and Other Postretirment Benefits Expected Benefit Payments [Line Items]
Expected future benefit payments, 2012	$ 23
Expected future benefit payments, 2013	26
Expected future benefit payments, 2014	22
Expected future benefit payments, 2015	16
Expected future benefit payments, 2016	20
Expected future benefit payments, 2017 - 2021	$ 127

The amount of the aggregate benefits expected to be paid in the five fiscal years thereafter (the aggregate amount of benefits expected to be paid in years 6 through 10 after the date of the latest statement of financial position).

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph f

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant