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Long-term Debt Including Unamortized Debt Discounts and Premiums (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Debt Instrument [Line Items]    
Senior Notes $ 1,432 $ 1,450
Senior Medium-Term Notes, Series A 249 249
Finance lease obligation 95 100
Junior Subordinated Notes   202
Total long-term debt $ 1,776 $ 2,001