Pension Benefits - Reconciliation of Fair Value Balances for Net Assets (Detail) (Pension Benefits [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year			$ 9,135	$ 7,800
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	11,495	10,755	9,135	7,800
Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	1,062	833
Assets Still Held at Reporting Date - Unrealized Gains/(Losses)	86	114
Assets Sold During the Year - Realized Gains/(Losses)	20	1
Purchases Sales and Settlements	(31)	114
Transfer In/(Out) of Level 3	0	0
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	1,137	1,062
Private Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	67	20
Assets Still Held at Reporting Date - Unrealized Gains/(Losses)	12	5
Purchases Sales and Settlements	35	42
Transfer In/(Out) of Level 3	0	0
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	114	67
Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	206
Assets Still Held at Reporting Date - Unrealized Gains/(Losses)	11	6
Purchases Sales and Settlements	7	200
Transfer In/(Out) of Level 3	0	0
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	224	206
Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	1,335	853
Assets Still Held at Reporting Date - Unrealized Gains/(Losses)	109	125
Assets Sold During the Year - Realized Gains/(Losses)	20	1
Purchases Sales and Settlements	11	356
Transfer In/(Out) of Level 3	0	0
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	1,475	1,335
Funds for Retiree Health Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	(42)	(31)
Assets Still Held at Reporting Date - Unrealized Gains/(Losses)	(1)	(3)
Purchases Sales and Settlements		(8)
Transfer In/(Out) of Level 3	0	0
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	(43)	(42)
Investments (Excluding Funds for Retiree Health Benefits) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	1,293	822
Assets Still Held at Reporting Date - Unrealized Gains/(Losses)	108	122
Assets Sold During the Year - Realized Gains/(Losses)	20	1
Purchases Sales and Settlements	11	348
Transfer In/(Out) of Level 3	0	0
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	$ 1,432	$ 1,293

Actual return on plan assets, separately identifying the amount related to assets sold during the period.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (d)(iv)(02)(A)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 5

-Subparagraph (c)(iv)(02)(A)

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Actual return on plan assets, separately identifying the amount related to assets still held at the reporting date.

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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.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

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-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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

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Amount of increase (decrease) in plan assets from purchases, sales and settlement of plan obligations.

+ References

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

-Publisher FASB

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-SubTopic 20

-Section 50

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Transfers in and out of Level 3. For example, transfers due to changes in the observability of significant inputs.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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