Available-For-Sale Securities (Amount Of Available-For-Sale Debt Securities By Maturity Periods) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Less than one year	$ 18
Available-for-sale debt securities, 1-5 years	136
Available-for-sale debt securities, 6-10 years	176
Available-for-sale debt securities, 11-15 years	42
Available-for-sale debt securities, 16-20 years	10
Available-for-sale debt securities, Over 20 years	245
Total Available-for-Sale Debt Securities	627
Rabbi Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Less than one year	0
Available-for-sale debt securities, 1-5 years	60
Available-for-sale debt securities, 6-10 years	31
Available-for-sale debt securities, 11-15 years	9
Available-for-sale debt securities, 16-20 years	5
Available-for-sale debt securities, Over 20 years	59
Total Available-for-Sale Debt Securities	$ 164

Amount of debt securities categorized neither as held-to-maturity nor trading.

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