Employee Benefits - Net Pension Cost and Amount Recognized in OCI for All Funded and Unfunded Plans (Detail) (Pension Plans [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on PBO	$ 46	$ 42	$ 47
Expected return on plan assets	(66)	(67)	(70)
Amortization of losses	16	19	16
Settlement loss	23	27
Net pension cost (benefit)	19	21	(7)
Other changes in plan assets and benefit obligations recognized in OCI:
Net (gain) loss	97	(106)	63
Amortization of losses	(39)	(46)	(16)
Total recognized in comprehensive income	58	(152)	47
Total recognized in net pension cost and comprehensive income	$ 77	$ (131)	$ 40