Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restoration Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of hours of service required to qualify for the plan	1,000 or more hours
Noncontributory and nonqualified plan, benefit expense	$ 20	$ 20	$ 31
Noncontributory and nonqualified plan, accrued benefits liabilities	175	164
Supplemental Executive Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan cost	22	33	31
Defined benefit plan obligation	$ 222	207
Defined Contribution Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employer contribution to match participant contribution in defined contribution plan, net	100.00%
Cost of defined benefit plans	$ 444	432	404
Defined benefit plan cost	21	25	$ 13
Defined benefit plan obligation	$ 111	$ 131
Defined Contribution Benefit Plans [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employer contribution to match participant contribution in defined contribution plan	3.00%
Defined Contribution Benefit Plans [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employer contribution to match participant contribution in defined contribution plan	9.00%