Change in Benefit Obligations (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Pension Plans, Defined Benefit
Defined Benefit Plan, Service Cost	$ 1,000,000	[1]	$ 1,000,000	[1]
Defined Benefit Plan, Interest Cost	29,000,000	[1]	31,000,000	[1]
Defined Benefit Plan, Expected Return on Plan Assets	51,000,000	[1]	50,000,000	[1]
Defined Benefit Plan, Amortization of Gains (Losses)	5,000,000	[1]	4,000,000
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	0		0
Defined Benefit Plan, Net Periodic Benefit Cost	(16,000,000)	[1]	(14,000,000)	[1]
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan, Service Cost	0		0
Defined Benefit Plan, Interest Cost	0		1,000,000
Defined Benefit Plan, Expected Return on Plan Assets	1,000,000		2,000,000
Defined Benefit Plan, Amortization of Gains (Losses)	0		(1,000,000)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(1,000,000)		0
Defined Benefit Plan, Net Periodic Benefit Cost	$ (2,000,000)		$ (2,000,000)

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