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Retirement Benefits (Changes In Fair Value Measurements Of Level 3 Investments) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Private Equity Partnerships [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value at January 1	$ 920	$ 795
Relating to assets still held at the reporting date	20	53
Relating to assets sold during the period	102	48
Purchases	96	146
Sales	224	122
Fair Value at December 31	914	920
Insurance Group Annuity Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value at January 1	2	3
Sales		1
Fair Value at December 31	$ 2	$ 2

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

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