Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016		Mar. 31, 2015
Pension Plan [Member]
Defined Benefit Plan, Service Cost	[1]	$ 1		$ 1
Defined Benefit Plan, Interest Cost	[1]	24		29
Defined Benefit Plan, Expected Return on Plan Assets	[1]	(46)		(51)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		0		0
Defined Benefit Plan, Amortization of Gains (Losses)	[1]	6		5
Defined Benefit Plan, Net Periodic Benefit Cost		(15)	[1]	(16)	[2]
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan, Service Cost		0		0
Defined Benefit Plan, Interest Cost		0		0
Defined Benefit Plan, Expected Return on Plan Assets		(1)		(1)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		(1)		(1)
Defined Benefit Plan, Amortization of Gains (Losses)		0		0
Defined Benefit Plan, Net Periodic Benefit Cost		$ (2)		$ (2)

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

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