Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2016		Jun. 30, 2015		Jun. 30, 2016		Jun. 30, 2015
Pension Plan [Member]
Defined Benefit Plan, Service Cost	[1]	$ 1		$ 1		$ 3		$ 2
Defined Benefit Plan, Interest Cost	[1]	24		29		49		58
Defined Benefit Plan, Expected Return on Plan Assets	[1]	(46)		(52)		(93)		(103)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		0		0		0		0
Defined Benefit Plan, Amortization of Gains (Losses)	[1]	6		6		12		11
Defined Benefit Plan, Net Periodic Benefit Cost		(15)	[1]	(16)	[1]	(29)	[1]	(32)	[2]
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan, Service Cost		0		0		0		0
Defined Benefit Plan, Interest Cost		0		1		1		1
Defined Benefit Plan, Expected Return on Plan Assets		(1)		(1)		(2)		(2)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		(1)		(2)		(3)		(3)
Defined Benefit Plan, Amortization of Gains (Losses)		0		0		0		0
Defined Benefit Plan, Net Periodic Benefit Cost		$ (2)		$ (2)		$ (4)		$ (4)

[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.