Change in Benefit Obligations (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Defined Benefit Plan, Plan Amendments			$ (76)
DefinedBenefitPlanFundedStatusOfPlan-Percent	104.94%	[1]	111.57%	[1]
Pension Plans, Defined Benefit
Pension and Other Postretirement Defined Benefit Plans, Liabilities	85		80
Defined Benefit Plan, Funded Status of Plan	145	[1]	298	[1]
Defined Benefit Plan, Service Cost	5	[1],[2]	5	[1],[2]	5	[2]
Benefit obligation, beginning of year	2,575	[1],[3]	2,838	[1]
Defined Benefit Plan, Interest Cost	124	[1],[2]	113	[1],[2]	119	[2]
Defined Benefit Plan, Contributions by Plan Participants	0	[1]	0	[1]
Defined Benefit Plan, Actuarial Gain (Loss)	401	[1]	(195)	[1]
Defined Benefit Plan, Benefits Paid	(165)	[1]	(181)	[1]
Defined Benefit Plan, Plan Amendments	0	[1]	0	[1]
Benefit obligation, end of year	2,935	[1],[3]	2,575	[1],[3]	2,838	[1]
Defined Benefit Plan, Administration Expenses	(5)	[1]	(5)	[1]
Defined Benefit Plan, Accumulated Benefit Obligation	2,935	[1]	2,575	[1]
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan, Funded Status of Plan	91	[4]	77	[4]
Defined Benefit Plan, Service Cost	0	[4]	0	[4]	0
Benefit obligation, beginning of year	81	[4]	167	[4]
Defined Benefit Plan, Interest Cost	3	[4]	6	[4]	7
Defined Benefit Plan, Contributions by Plan Participants	11	[4]	21	[4]
Defined Benefit Plan, Actuarial Gain (Loss)	(10)	[4]	1	[4]
Defined Benefit Plan, Benefits Paid	(17)	[4]	(41)	[4]
Defined Benefit Plan, Plan Amendments	0	[4]	(76)	[4]
Benefit obligation, end of year	69	[4]	81	[4]	167	[4]
Defined Benefit Plan, Administration Expenses	$ 0	[4]	$ 0	[4]

[1] 1 Employer contributions represent the benefits that were paid to nonqualified plan participants. SERPs are not funded through plan assets.

[2] 1 Administrative fees are recognized in service cost for each of the periods presented.

[3] 3 Includes $85 million and $80 million of benefit obligations for the unfunded nonqualified supplemental pension plans at December 31, 2014 and 2013, respectively.

[4] 2 Plan remeasured at December 31, 2013 due to plan amendment.