Defined Benefit Retirement Plans with Overfunded and Underfunded Status (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Change In Fair Value Roll Forward [Abstract]
Fair value of plan assets at January 1	$ 181
Fair value of plan assets at December 31	185	181
Defined Benefit Plan, Change in Benefit Obligation
Defined Benefit Plan, Interest Cost	10	11	12
Underfunded Defined Benefit Pension Plans
Defined Benefit Plan Change In Fair Value Roll Forward [Abstract]
Fair value of plan assets at January 1	181	197
Actual return on plan assets	21
Contributions	4	4
Settlement	(10)	(10)
Benefits paid	(11)	(10)
Fair value of plan assets at December 31	185	181
Defined Benefit Plan, Change in Benefit Obligation
Projected benefit obligation at January 1	253	227
Defined Benefit Plan, Interest Cost	10	11
Settlement	(10)	(10)
Actuarial loss	14	35
Benefits paid	(11)	(10)
Projected benefit obligation at December 31	256	253
Underfunded projected benefit obligation recognized in the Consolidated Balance Sheet as a liability	$ (71)	$ (72)

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The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable.

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Amount of gain (loss) from a decision to temporarily deviate from the substantive plan, or from a change in benefit obligation or plan asset value from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover or salary scale.

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1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.

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The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets.

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The increase in the fair value of plan assets from contributions made by the employer.

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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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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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If aggregate disclosures are presented, the aggregate benefit obligation for plans with benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.

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The amount of decrease that relates to an irrevocable action that relieves the employer (or the plan) of primary responsibility for a benefit obligation and eliminates significant risks related to the obligation and the assets used to effect the settlement. Examples of transactions that constitute a settlement include (a) making lump-sum cash payments to plan participants in exchange for their rights to receive specified benefits and (b) purchasing nonparticipating annuity contracts.

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