Investments (Schedule Of Cost And Fair Value Of Equity Securities) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Cost	$ 447	$ 440
Gross unrealized appreciation	99	83
Gross unrealized depreciation	(10)	(13)
Fair value	$ 536	$ 510

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Section 45

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 320

-Section 50

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