Employee Benefits - Net Pension Cost and Amount Recognized in OCI for All Funded and Unfunded Plans (Detail) - Pension Plans [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Interest cost on PBO	$ 44	$ 41	$ 46
Expected return on plan assets	(58)	(56)	(66)
Amortization of losses	17	18	16
Settlement loss	18	23	23
Net pension cost (benefit)	21	26	19
Other changes in plan assets and benefit obligations recognized in OCI:
Net (gain) loss	(9)	47	97
Amortization of gains	(35)	(41)	(39)
Total recognized in comprehensive income	(44)	6	58
Total recognized in net pension cost and comprehensive income	$ (23)	$ 32	$ 77