Defined Benefit Plan, Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014		Sep. 30, 2015		Sep. 30, 2014
Pension Plans, Defined Benefit
Defined Benefit Plan, Service Cost	[1]	$ 2	$ 2		$ 4		$ 4
Defined Benefit Plan, Interest Cost		29	31	[1]	87	[1]	93	[1]
Defined Benefit Plan, Expected Return on Plan Assets	[1]	(52)	(50)		(155)		(150)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		0	0		0		0
Defined Benefit Plan, Amortization of Gains (Losses)	[1]	5	4		16		12
Defined Benefit Plan, Net Periodic Benefit Cost		(16)	(13)		(48)		(41)
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan, Service Cost		0	0		0		0
Defined Benefit Plan, Interest Cost		1	1		2		2
Defined Benefit Plan, Expected Return on Plan Assets		(2)	(1)		(4)		(4)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		(1)	(2)		(4)		(4)
Defined Benefit Plan, Amortization of Gains (Losses)		0	0		0		0
Other Postretirement Benefit Expense		$ (2)	$ (2)		$ (6)		$ (6)

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