Investments (Schedule Of Cost And Fair Value Of Equity Securities) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Cost	$ 781	$ 707
Gross unrealized appreciation	55	41
Gross unrealized depreciation	(4)	(4)
Fair value	$ 832	$ 744

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

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